In the smoldering geopolitical feud between the U.S. and Iran, spymaster Major-General Qasem Soleimani is emerging as director of the Islamic Republic´s effort to spread its influence abroad and bedevil the West.

In January, Gen. Soleimani—commander of Iran´s elite overseas forces— traveled in secret to Damascus to meet with Syria´s president and architect of that nation´s bloody and continuing Arab Spring crackdown. At the meeting, Gen. Soleimani agreed to send more military aid and reaffirmed Iran´s close friendship, according to U.S. and Arab officials.

In February, American officials detected four Iranian jets ferrying munitions to Syria. On Sunday the Obama administration announced it would start providing communications equipment to Syria´s opposition, while Arab states committed to paying the salaries of rebel fighters.

While it is tough to know the precise inner workings of Iran´s political machine, Gen. Soleimani´s role in Syria is the latest indication that he ranks among the most important figures driving Iranian policy.

Senior U.S. and Arab officials say it was Gen. Soleimani´s idea to harass and bleed American forces for years in Iraq by arming Shiite militias there. The general´s elite Qods Force of soldiers and spies oversees Iran´s support for groups fighting Israel, including Hezbollah and Hamas.

Israel publicly blames the Qods Force for a string of assassination attempts on Israeli diplomats; U.S. officials have publicly blamed Iran and privately point a finger at the Qods Force. Last October, the U.S. Justice Department indicted Gen. Soleimani in the Southern District of New York for his purported role in a bomb plot aimed at killing the Saudi Arabian ambassador at a cafe in Washington, D.C. Iran has denied the charges.

U.S. officials believe Mr. Soleimani´s approval underlies any Qods Force operations outside Iran. They have tied Iran´s Qods Force to recent bombings in Thailand and India, as well as alleged plotting in Azerbaijan.

"He´s a deep strategic thinker, but believes he should be a martyr" for Iran´s Islamic revolution, said Mowwafak al-Rubaie, Iraq´s former national security adviser, who has met Gen. Soleimani three times in Tehran in recent years.

Lightly bearded, 55 years old and often wearing a collarless business shirt or military uniform, Gen. Soleimani has a calm presence about him, according to people who have met him. American and British intelligence officials draw comparisons between the real-life Iranian general and the fictional Soviet spymaster Karla, of John le Carre´s Cold War novels. Global chess masters both, their goal is to blunt U.S. advances while aligning with Washington´s adversaries.

At times, Gen. Soleimani has communicated directly with American military planners. In early 2008, Gen. Soleimani passed a message to then-commander of U.S. forces in Iraq, Gen. David Petraeus, via Iraqi politician Ahmad Chalabi. "General Petraeus, you should know that I, Qasem Soleimani, control the policy for Iran with respect to Iraq, Lebanon, Gaza and Afghanistan," he said, according to an official familiar with the incident.

His leadership of the Qods Force, the international arm of the Islamic Revolutionary Guard Corps, gives him a unique portfolio of duties, U.S. and Mideast officials say: intelligence operative, diplomat, foreign-policy strategist, battlefield commander and, allegedly, terrorism planner.

"I see [Gen. Soleimani] as sort of the evil genius behind all of the activities that Qods Force has done, all the expansion of Iranian influence," said Richard Clarke, counterterrorism czar for Presidents Bill Clinton and George W. Bush.

Attempts to reach Gen. Soleimani through Iran´s mission to the United Nations were unsuccessful. Tehran denies any role in supporting international terrorism or providing arms to the government of Syrian President Bashar al-Assad. Iran accuses Israel of overseeing the assassinations of five Iranian nuclear scientists in recent years, a charge the Jewish state has neither denied nor confirmed.

Gen. Soleimani grew up in a poor family in Iran´s southeast Kerman province, an area known for the central government´s limited writ and for the power of its local tribes, according to researchers who have studied the commander´s rise. As a young man he worked at menial construction jobs before joining the Revolutionary Guards, the armed- services branch responsible for enforcing the ideology behind Iran´s 1979 Islamic revolution.

Within the Revolutionary Guards, he joined the Qods Force—the organization he now oversees. His background prepared him for his future operating in the tribal societies of Iraq and Afghanistan, said Ali Alfoneh, who studies Gen. Soleimani as a researcher at the American Enterprise Institute in Washington.

Gen. Soleimani spent his early years in the Qods Force combating Central Asian narcotics smugglers and the Taliban government in Afghanistan. Gen. Soleimani took over the Qods Force in the late 1990s after establishing a reputation for his fighting during the 1980-88 Iran-Iraq war, according to Mr. Alfoneh and other academics.

In the months following the Sept. 11, 2001, terror attacks on the U.S., he emerged as a surprising U.S. ally, says Hossein Mousavian, a Princeton University-based researcher who served on Iran´s Supreme National Security Council with Gen. Soleimani at that time. Gen. Soleimani was among those on the council who advocated cooperating with the U.S. to topple the Taliban. Iranian and American diplomats held regular meetings to devise ways to bring now-President Hamid Karzai to power, according to diplomats from both countries.

"Qasem is a very pragmatic commander," said Mr. Mousavian, who fell out with Iranian President Mahmoud Ahmadinejad following the diplomat´s role as an Iranian nuclear negotiator in the early 2000s. "He´s willing to cooperate with the West if it serves Iran´s interests."

Messrs. Mousavian, Al-Rubaie and others who have met the general describe him as both religious and pragmatic, but differ on his ultimate willingness to make peace with the U.S. Mr. Mousavian says the general wants the West to recognize Tehran´s role as a Mideast power. Others see him as a revolutionary who will never accept rapprochement with the "Great Satan."

The fragile post-9/11 alliance between Iran and the U.S. collapsed with the U.S. invasion of Iraq in 2003. Both Washington and Tehran viewed Saddam Hussein as a threat but had very different views on who or what should succeed him.

Iran wanted the U.S. to quickly withdraw from Iraq and install a provisional government led by Shiites and Kurds with ties to Tehran. Instead, the Bush administration set up a formal occupation force and a military presence that stayed in Iraq for seven years.

The U.S.´s military occupation set the stage for what U.S. and Iraqi officials say was the Qods Force´s aiding and arming of the militias in Iraq that harassed U.S. and allied forces there for much of the past decade. Beginning in 2004, American and Iraqi intelligence detected fighters traveling over Iraq´s southeastern border into Iran for training with Qods Force and Hezbollah operatives. The Iraqis were schooled in small arms and roadside bombs, which became the biggest killer of American soldiers during the war.

The Iran-trained fighters also received religious schooling and were advised to follow the teachings of the founder of the modern Islamic state of Iran, Ayatollah Ruhollah Khomeini, according to fighters who were captured and interrogated by the U.S. military, Pentagon transcripts indicate. A number of the trainees told their American questioners that they had no love for the Qods Force or the Iranian system, but needed their assistance to fight the U.S. occupation.

As the battle against the militias wore on, U.S. officials voiced frustration that many of their allies within Iraq—including Iraq´s president, Jalal Talabani—maintained their long-standing ties to Gen. Soleimani. Kurdish leaders such as Mr. Talabani cooperated with Iran during Saddam Hussein´s rule in an effort to obtain independence from Baghdad.

"General Petraeus mentioned that we continue to see on average one rocket and one [armor-piercing bomb] attack daily," a State Department diplomat wrote from Baghdad in 2009, according to a cable obtained by the Internet site WikiLeaks. "The next time Talabani spoke to Qasem Soleimani, he might pass along that we are concerned about Iranian actions," the cable said.

In addition to Mr. Talabani, other close allies of the Bush administration also knew Gen. Soleimani, including Mr. Chalabi, the Iraqi Shiite politician who shared a hatred of Saddam Hussein with the Iranians. In the weeks before the U.S. invasion of Iraq, Mr. Chalabi traveled between Washington and Tehran and briefed Gen. Soleimani on U.S. objectives, according to Francis Brooke, an aide to the Iraqi politician.

At times, Gen. Soleimani´s Iraqi and Lebanese allies engaged in direct conflict with U.S. forces inside Iraq, said American officials. In January 2007, four American soldiers were captured and executed in the central Iraqi city of Karbala in an operation the Pentagon believed was jointly run by the Qods Force, Hezbollah and Iraqi militants.

Later that year, the Pentagon captured two Iraqi brothers and a Hezbollah commander in southern Iraq who allegedly admitted to cooperating with Gen. Soleimani´s Qods Force, after initially pretending to be a mute, according to military officials briefed on the operation.

With the end of the Iraq war—and the spread of Arab Spring popular uprisings across the region over the past year—the U.S.´s conflict with Gen. Soleimani and the Qods Force has expanded into new territory. The U.S. publicly alleges that Iran has been working to overthrow American allies in Yemen, Lebanon and Bahrain. Tehran has accused Washington of propping up Arab monarchs and despots in the Persian Gulf to protect U.S. energy and security interests.

The center of this conflict now is Syria, where Iran´s closest Arab ally, President Assad, is facing a broad challenge to his family´s 40- year rule.

For the U.S., the goal of ending the Assad regime is primarily prompted by the opportunity to weaken Iran. Mr. Assad´s fall, U.S. officials believe, would cripple Iran´s ability to funnel arms to allies in Lebanon and the Palestinian territories. The Obama administration hopes the Syrian uprising will rekindle an Iranian protest movement that was suppressed by Tehran´s security forces in 2009.

The Qods Force has long had a presence in Damascus due to Iran´s and Syria´s joint efforts to arm Hezbollah and Hamas. Ever since the Arab Spring uprisings began last year, the Qods Force has been advising Syria´s security forces on crowd control and on technologies needed to track political activists, according to U.S. officials and Syrian activists.

Since Gen. Soleimani´s January visit to Damascus, U.S. and Arab officials said Tehran appears to have upped its support for the Syrian regime.

Mr. Assad´s forces have been trying to crush Syria´s opposition by overrunning its strongholds in the cities of Homs, Hama and Idlib. According to U.S. officials briefed on Syria intelligence, the Qods Force has been accelerating shipments of small arms and artillery to support that effort. Some of these arms have been ferried into Syria on Iranian Iluyshin jets controlled by the Qods Force, according to an American official briefed on the intelligence.

"Soleimani has emerged as public enemy No. 1 in the Arab Spring," said a senior administration official working on Syria.

The Obama administration, following the efforts of its predecessors, is trying to curtail the ability of Gen. Soleimani to project influence across the Middle East, senior U.S. officials said. The U.S. Treasury has placed sanctions on the Qods Force commander three times; those sanctions remain in place. The U.S. and European Union are also seeking to block the Revolutionary Guard´s ability to ship or fly arms into Syria, Lebanon and the Palestinian territories.

Last week, the Treasury sanctioned an Iranian airline, Yas Air, for allegedly ferrying arms to Damascus and specifically argued that the airline is controlled by the Qods Force.

A spokesman for Yas Air said all its flights are in accordance with international aviation law.

Last October, a former Central Intelligence Agency spy, Reuel Marc Gerecht, testified before Congress that if the Qods Force´s role in last year´s alleged plot to kill the Saudi ambassador is proven, the U.S. "should hold Qasem Soleimani responsible…. Go get him, either try to capture him or kill him."

Iran´s government responded by calling for the international policing body, Interpol, to arrest Mr. Gerecht. More than 200 Iranian lawmakers signed a statement of support for Gen. Soleimani. And on Farsi-language websites, hard-line Iranian groups launched a campaign behind the slogan: "We Are All Qasem Soleimani."

Write to Jay Solomon at jay.solomon@wsj.com and Siobhan Gorman at siobhan.gorman@wsj.com (Copyright © Dow Jones & Company, Inc.) 04/04/12)