AMMAN, Jordan — Iran signaled a willingness on Tuesday to allow potentially intrusive international inspections of secret military facilities, raising expectations that it was searching for a diplomatic solution to the standoff over its nuclear program.

With talks between Iran and six global powers set to begin Wednesday in Baghdad, the director general of the International Atomic Energy Agency, Yukiya Amano, said he had reached something of a breakthrough with Iranian officials on the agency’s longstanding request for access to the facilities. Mr. Amano’s assertion suggested that Iran was seeking to set a positive tone for the nuclear talks and perhaps ease pressure from strict Western-led sanctions that are about to become even more severe.

Mr. Amano did not specify a timetable or other details. Iran’s critics were quick to suggest that the conciliatory-sounding signal from Iran could amount to little more than a negotiating tactic as the Iranians prepare for talks on the more complex issue of Iran’s uranium enrichment with the six powers — the permanent members of the United Nations Security Council plus Germany.

But Mr. Amano told reporters at the atomic agency’s headquarters in Vienna that there had been an “important development” in the agency’s effort to reach a “structured agreement” on how its inspectors would conduct an investigation into whether the Iranians had sought ways in the past to weaponize enriched nuclear fuel, a longstanding suspicion by the United States, Israel and the European Union.

“The decision was made to conclude and sign the agreement,” said Mr. Amano, who visited Tehran on Sunday and Monday — his first trip there since his appointment in 2009. He has expressed strong suspicions himself about what he has called Iran’s lack of cooperation in its dealings with the agency.

Mr. Amano’s upbeat assessment, coming on top of recent optimistic signals from Western diplomats, suggested that Iran’s chief negotiator, Saeed Jalili, was signaling Iran’s sincerity in talks with the six powers — the United States, France, Britain, Germany, Russia and China — on a more wide-ranging deal to bring Iran back into compliance with Security Council resolutions and ensure that Iran is not trying to build a nuclear weapon.

The most immediate goal of the Baghdad talks for the six appears to be to get an agreement by Tehran to stop enriching uranium to 20 percent purity — near the level required for a nuclear weapon — and to discuss exporting its stockpile of uranium enriched to that level. And the six want to be sure Iran is doing more than public relations and is prepared to move quickly to take concrete steps to calm global and regional concerns.

The Baghdad talks were expected to get under way about noon, with a plenary session where the six powers will present a detailed proposal to Iran on concrete confidence-building steps and hear an Iranian presentation before a break for lunch and more discussions, said a senior Western official, who requested anonymity because of the delicacy of the talks.

The official cautioned that an I.A.E.A. agreement with Iran on how to proceed to settle outstanding issues from the past would be good news but would take time to turn into action. The agency, the official said, is trying to get a picture of Iran’s past program, but the Baghdad negotiations are about divining Iran’s intentions and bringing the country into full compliance. “These are two separate processes,” the official said.

The White House welcomed Mr. Amano’s announcement with caution. “It’s an agreement in principle that represents a step in the right direction,” said Jay Carney, the White House press secretary. “But as we’ve said in the past about the totality of Iran’s obligations and their fulfillment of them, we will make judgments about Iran’s behavior based on actions, not just promises or agreements.”

Even Mr. Amano said the talks had not yet produced an agreement on how the I.A.E.A. could conduct the inspections and interviews it demands. “There remain some differences,” Mr. Amano said, but he noted that Mr. Jalili had told him that those differences “will not be the obstacle to reaching agreement.”

In past meetings with the six, Mr. Jalili has argued that Iran’s compliance with the I.A.E.A. meant that sanctions should be lifted. That may be an argument he renews Wednesday.

Iran’s state-run news media noted that no deal had been made so far with Mr. Amano, and focused instead on what the government has portrayed as steady Iranian advances in nuclear and rocket technology. Iran state television said scientists had successfully loaded uranium fuel into a medical isotope reactor on Tuesday, and the Islamic Republic News Agency said Iran would launch a satellite on Wednesday with an upgraded model of its Safir 2 rocket. The United States and its allies have expressed concern that such a rocket could be altered to carry a warhead.

The negotiations with Iran on its nuclear program so far have been talks about talks. In Baghdad, American and European officials hope to begin the talks themselves — to start negotiating about what Iran must do to ease global concerns that it is developing a nuclear weapon, and then proceed through a series of detailed meetings and negotiations over the next few months.

Iranian officials are eager for the United Nations, the United States, the European Union and their allies to lift economic sanctions that are clearly hurting Tehran. But Western officials have emphasized in recent days that any removal of sanctions — or postponement of sanctions on oil exports that take effect July 1 — will require concrete action by Iran of the kind that the Baghdad meeting alone is unlikely to yield.

If the Baghdad talks produce progress, American officials have said, they are prepared to offer some easing of existing restrictions on the imports of airplane parts, technical assistance to Iran’s lagging energy industry, help with nuclear safety and even counternarcotics, or firm statements of Iran’s right under the Nuclear Nonproliferation Treaty to a peaceful nuclear program so long as it meets international safeguards.

But if the sanctions are a prime reason for Iran to negotiate seriously, Western officials said, they must not be removed prematurely. Even more, they argue, the impending embargo on Iran’s oil exports is another incentive for Iran to grapple seriously with the problem and not play for time.

A senior European diplomat who was not authorized to discuss the talks publicly said Iran’s uranium enrichment to 20 percent purity is a particular concern, since the stockpile reduces considerably the “breakout” period should Iran decide to assemble a nuclear weapon. It represents an especially delicate issue for Israel, which has said that it would act militarily, if necessary, to stop Iran from building a nuclear weapon.

The Israeli defense minister, Ehud Barak, reacted skeptically to Mr. Amano’s talk of an agreement. “It appears that the Iranians are trying to attain a technical agreement to create the illusion of progress in the talks, in order to relieve some of the pressure ahead of tomorrow’s discussions in Baghdad and to push back at the sharpening sanctions,” Mr. Barak said in an e-mailed statement. “Israel believes that Iran must be placed in an unequivocally clear position where there won’t be any window or crack for it to advance toward nuclear weapons.”

Reporting was contributed by Alan Cowell from Paris, Jodi Rudoren from Jerusalem, Thomas Erdbrink from Tehran, Paul Geitner from Brussels, Peter Baker from Washington, and Rick Gladstone and William J. Broad from New York. (Copyright 2012 The New York Times Company 05/23/12)