* Republican candidate seeks support from Jewish voters
* Romney takes tough stance on Iran in foreign policy speech
* Aide: Romney would back Israeli strike over Iran nuclear capability
By Steve Holland
JERUSALEM, July 29 (Reuters) - U.S. Republican candidate Mitt Romney, presenting himself as Israel's best friend in the Nov. 6 presidential election, said on Sunday that "any and all measures" must be used to keep Iran from developing a nuclear weapon.
A top aide said Romney would support an Israeli military strike if all options had been exhausted, but the candidate himself balked at repeating that position.
In a foreign policy speech in Jerusalem, Romney voiced strong support for the alliance between the United States and Israel and seemed to suggest that President Barack Obama had let the relationship flounder.
"We cannot stand silent as those who seek to undermine Israel voice their criticisms. And we certainly should not join in that criticism. Diplomatic distance in public between our nations emboldens Israel's adversaries," said Romney, the walls of the Old City lining the hilltop behind him.
The former Massachusetts governor was in Jerusalem on the second leg of a trip to strengthen his foreign policy credentials in his race to unseat Obama.
"We should employ any and all measures to dissuade the Iranian regime from its nuclear course, and it is our fervent hope that diplomatic and economic measures will do so. In the final analysis, of course, no option should be excluded. We recognize Israel's right to defend itself, and that it is right for America to stand with you," he said.
Though he adopted an aggressive tone, Romney did not go as far as his senior foreign policy advisor, Dan Senor, who said earlier: "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 aide's comments put Romney at odds with Obama's efforts to press Israel to avoid any pre-emptive strike before tough Western economic sanctions against Iran run their course.
Romney, however, refused to repeat them when asked by CBS' "Face the Nation."
"Well I think because I'm on foreign soil I don't want to be creating new foreign policy for my country or in any way to distance myself in the foreign policy of our nation. But we respect the right of a nation to defend itself," Romney said.
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 military strike.
'STRONG MILITARY THREAT'
The presidential hopeful was greeted warmly earlier by Israeli Prime Minister Benjamin Netanyahu, an old friend of his, who has at times had a strained relationship with Obama.
Netanyahu issued his customary call for stronger measures behind the sanctions to prevent Iran from developing an atomic bomb, which Israel says would be a threat to its existence. Iran says its nuclear program is for peaceful purposes.
"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 uranium enrichment facilities buried deep underground will be invulnerable to bombing.
U.S. Defense Secretary Leon Panetta , arriving in Tunisia at the start of a week-long trip to the Middle East and North Africa, defended U.S.-Israeli defense cooperation under Obama.[ID :nL2E8IR6Q4]
"I'm not going to comment on what political candidates say or don't say," Panetta said.
"I'm proud of the defense partnership that we've built over the past several years. The U.S.-Israel defense relationship, I believe, is stronger today than it has been in the past," the Pentagon chief told reporters traveling with him.
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.
Panetta said his view is that the Israelis "have not made any decisions with regards to Iran and that they continue to support the international effort to bring pressure against Iran."
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.
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 Jewish voters and pro-Israel evangelical voters and contrast himself with Obama.
Romney has sharply criticised Obama's handling of Iran as not being tough enough.
After talks with Israeli leaders, Romney met Palestinian Prime Minister Salam Fayyad. He then visited 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 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 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.