By Dan Williams

JERUSALEM (Reuters) - The United States' top military officer arrives in Israel on Thursday as the allies coordinate efforts to curb Iran's nuclear program - and play down suggestions they are at odds on strategy.

The United States, which is leading Western pressure on Tehran to curb controversial uranium enrichment, has voiced concern that the Israelis could attack their foe preemptively and deepen instability in an already volatile region.

This week's postponement of joint military maneuvers - and sharp remarks in Washington disowning the killing of an Iranian nuclear scientist which many suspect was the work of Israeli agents - have fueled speculation that General Martin Dempsey, chairman of the Joint Chiefs of Staff, may be flying in from Europe to lay down the law and rein in his close ally.

Officials on both sides rejected that idea: "Chiefs of staff deal with preparing their militaries for various options," Israeli Defense Minister Ehud Barak said on Wednesday.

"They don't deal in passing diplomatic messages."

Barak also said that any decision about an Israeli attack on Iran was "very far off." Like the United States, Israel does not believe Iranian assurances that its nuclear research has no military purpose. It says it would use force to prevent the Islamic Republic from acquiring atomic weapons that Israel believes would threaten the survival of the Jewish state.

Along with an unusually dovish comment last week from Prime Minister Benjamin Netanyahu that U.S.-led economic sanctions against Iran appeared to be having an effect, Barak's remarks appeared designed to counter suggestions that Israel was losing patience with U.S. President Barack Obama's diplomatic approach.

Both sides also insisted that they postponed a joint air defense exercise, planned for May, for operational reasons that were entirely unrelated to the situation with Iran.

FRICTION

A record of barely concealed friction between Netanyahu's right-wing coalition and the Democrat in the White House has added to speculation about differences over Iran - differences which are now particularly sensitive as Obama campaigns for re-election in November and faces criticism from some U.S. voters for lacking vigor in his support for Israel.

Barak further played down the importance of Dempsey's first visit to Israel in his current capacity by noting that, as Israeli defense minister, he was in regular direct contact with his U.S. counterpart, Defense Secretary Leon Panetta.

"The dialogue between us is conducted on the basis of mutual respect," Barak said. "This administration gives unprecedented support to Israel's defense establishment."

A U.S. official said that Dempsey, who was to arrive on Thursday evening for a stopover after a European trip, was "meeting with counterparts and important close allies, regardless of any current political situations." He will leave again on Friday as Israel shuts down for the Jewish sabbath.

Iran denies seeking the bomb, but its secretive nuclear projects and advances in ballistic missile development have drawn international censure and sanctions. The U.S. navy has also maneuvered in the Gulf in the face of an Iranian threat to blockade the Strait of Hormuz, a strategic oil-export channel.

Israel, which is presumed to have the only nuclear arsenal in the Middle East, has urged Washington to stiffen penalties on Iran's energy sector and central bank, and hinted it could resort to unilateral attacks if it deems diplomacy a dead end.

Such differences between the allies have been seized upon by Obama's Republican rivals ahead of this year's presidential election. The incumbent says he is determined to rein in Iran and has sought to burnish his pro-Israel credentials.

A senior Israeli official played down the unilateral Israeli "military option" on Thursday and appealed to U.S. interests in a Middle East where the popular Arab uprisings have shaken U.S.-aligned leaders, some of whom, like those in the Gulf, share Israeli and Western views of Iran as a threat.

"America is, to my regret, perceived in the Arab world as a country that has become weak and may be unable to provide them with the protection they desire in the face of Iran," Deputy Prime Minister Dan Meridor told Army Radio.

Should the Obama administration succeed in rolling back such perceptions among its Arab allies, Meridor said, it "would shore up their status, which is so important -- important for them and, by the way, for us -- in the Arab world."

(Writing by Dan Williams; Editing by Alastair Macdonald)