(Reuters) - U.S. Republican presidential candidate Mitt Romney would support an Israeli decision to use military force to stop Iran from developing a nuclear weapon, a senior aide said on Sunday.

Romney met with Israeli Prime Minister Benjamin Netanyahu in Jerusalem on the second leg of a trip show display his foreign policy credentials in his race to unseat President Barack Obama in the November 6 election.

Shortly before talks with Netanyahu, Romney´s senior national security aide, Dan Senor, told reporters travelling with the candidate:

"If Israel has to take action on its own, in order to stop Iran from developing that capability, the governor would respect that decision."

The comment seemed to put Romney at odds with Obama´s efforts to press Israel to avoid any preemptive strike before tough Western economic sanctions against Iran run their course.

Senor later expanded on his remarks, saying Romney felt "we should employ any and all measures to dissuade the Iranian regime from its nuclear course".

It was Romney´s "fervent hope that diplomatic and economic measures will do so" and "no option should be excluded", Senor said, adding that "Romney recognizes Israel´s right to defend itself, and that it is right for America to stand with it".

Standing beside Netanyahu at the Israeli leader´s office, Romney said only that Iran´s effort to become a nuclear power "is one which I take with great seriousness".

The failure of talks between Iran and six world powers to secure a breakthrough in curbing what the West fears is a drive to develop nuclear weapons has raised international concern that Israel may opt for a go-it-alone military strike.

Netanyahu issued his customary call for stronger measures behind the sanctions to curb Iran´s program, which Israel sees as a threat to its existence. Iran says its project is for peaceful purposes.

"STRONG MILITARY THREAT"

"We have to be honest that sanctions have not set back the Tehran program one iota and that a strong military threat coupled with sanctions are needed to have a chance to change the situation," Netanyahu said.

Israel, widely assumed to be the Middle East´s only nuclear-armed state, has warned it is only a matter of time before Iran´s nuclear program achieves a "zone of immunity" in which bombs will not be able to effectively strike uranium enrichment facilities buried deep underground.

Though Washington has been pressing Israel not to launch a solo strike on Iran, Obama has not ruled out military action if diplomacy fails to curb Iran´s nuclear drive.

The Israeli newspaper Haaretz said on Sunday that Obama´s national security adviser had briefed Netanyahu on a U.S. contingency plan to attack Iran. A senior Israeli official denied the report..

In an effort that appeared timed to upstage Romney´s visit to Israel, Obama signed a measure on Friday to strengthen U.S.-Israeli military ties and Defense Secretary Leon Panetta is expected to visit Israel later this week.

Romney´s overseas tour got off to a rocky start, when he angered the British by questioning whether London was ready for the Olympics, a statement he was forced to clarify after a rebuke from Prime Minister David Cameron.

His visit to Israel gives him the opportunity to appeal to both Jewish voters and pro-Israel evangelical voters and contrast himself with Obama, who has a strained relationship with Netanyahu.

Romney has sharply criticized Obama´s handling of Iran as not being tough enough.

According to excerpts of a speech Romney was to deliver on Sunday evening, the former Massachusetts governor planned to say that an aggressive approach to Tehran was needed to protect against a threat to the very existence of Israel, the closest U.S. ally in the turbulent Middle East.

"When Iran´s leaders deny the Holocaust or speak of wiping this nation off the map, only the naïve - or worse - will dismiss it as an excess of rhetoric," the text of the speech included.

"Make no mistake: the ayatollahs in Tehran are testing our moral defenses. They want to know who will object, and who will look the other way."

"My message to the people of Israel and the leaders of Iran is one and the same: I will not look away; and neither will my country," the text said.

After his meeting with Netanyahu, Romney met with President Shimon Peres, opposition head Shaul Mofaz and Palestinian Prime Minister Salam Fayyad. He then headed to the Western Wall, Judaism´s most revered site.

Wearing a black Jewish skullcap and surrounded by a determined throng of security personnel who cleared a path for him, Romney carefully navigated his way through hundreds of worshippers, some of whom shouted out cries of support.

Romney ends his trip on Monday with a fundraiser for a crowd of mostly Jewish Americans who live in Israel.

The Romney campaign initially had declared the fundraiser off limits to reporters, but on Sunday said it would allow press coverage after journalists complained the campaign was reneging on a prior agreement to open more of its finance events. (Writing by Steve Holland and Maayan Lubell; Editing by Allyn Fisher-Ilan and Michael Roddy)(© Thomson Reuters 2012. 07/29/12)