Sen. Barack Obama (D-Ill.) is engaged in a concerted effort to reassure Jewish leaders in the face of an increasingly aggressive Republican campaign to question his tolerance and his commitment to supporting Israel.

In a typical attack, the Tennessee Republican Party, under the headline "Anti-Semites for Obama," said Monday that it was joining "a growing chorus of Americans concerned about the future of the nation of Israel, the only stable democracy in the Middle East, if Sen. Barack Hussein Obama is elected president of the United States."

Two controversial Chicago figures -- Nation of Islam leader Louis Farrakhan and the Rev. Jeremiah Wright, pastor of Obama's church -- have figured prominently in the criticism of Obama. In Tuesday's Democratic debate in Cleveland, Obama disavowed an endorsement from Farrakhan but did not directly answer a question about Wright once having said that Farrakhan "epitomizes greatness."

Asked by moderator Tim Russert what he could do to reassure Jewish Americans, Obama cited his belief that Israel's security is "sacrosanct." He also said he has strong support in the Jewish community because of his opposition to anti-Semitism and his efforts to rebuild the relationship between Jews and African Americans.

On Sunday, Obama took time from his campaign to air out concerns with about 100 Jewish leaders in Cleveland, assuring them of "an unshakable commitment to the security of Israel and the friendship between the United States and Israel."

After the meeting, Rabbi Michael Lerner, editor of the liberal Jewish magazine Tikkun, issued a statement declaring that Obama "has been very successful . . . in reassuring the bulk of American Jews that the innuendoes and overt attacks on his alleged hostility to or indifference to the well-being of Israel are false."

To some Jewish leaders, even ones who have remained neutral in the presidential campaign, Obama's struggles are exasperating. Abraham H. Foxman, national director of the Anti-Defamation League, said yesterday from Jerusalem that Obama has gone much further than other black leaders in his denunciation of Farrakhan and has recently expressed stalwartly pro-Israel views.

"As far as I'm concerned, this issue is behind us," said Foxman, who has not endorsed a candidate. "But with the Internet, as all Jews should know, these things have a half-life. They just keep going."

Rep. Stephen I. Cohen (D-Tenn.), one of about half a dozen announced Jewish Obama supporters in the House, noted that Obama had gone to Atlanta's Ebenezer Baptist Church on Martin Luther King Day to speak out against anti-Semitism in the African American community. But he and other Jewish Democrats expressed concern that perception and innuendo could be taking a toll among Jewish voters, some of whom could shift allegiances to Sen. John McCain (Ariz.), the presumptive Republican nominee, in November.

In the Democratic presidential primaries, Sen. Hillary Rodham Clinton (N.Y.) has run well ahead of Obama among Jewish voters in states with large Jewish populations, taking 67 percent of the Jewish vote in Nevada, 63 percent in New Jersey, 65 percent in New York and 60 percent in Maryland. Obama narrowly won the Jewish vote in Arizona, California and Massachusetts, and captured 61 percent in Connecticut.

"The campaign's going to have to make a strong effort against these rumors," Cohen said.

Alan Solomont, a Boston financier who is Obama's Northeastern finance chairman, said he has been fielding almost daily calls from Jewish friends, asking about Obama's position on Israel and on other policy issues important to them.

Another issue for Obama besides Farrakhan and White has been his campaign's association with Zbigniew Brzezinski and Robert Malley, two prominent foreign policy experts whom some Jews regard as anti-Israel.

Obama took on those issues in Cleveland when he told Jewish leaders that Brzezinski, a national security adviser to President Jimmy Carter, is not a key adviser but merely someone he had lunch with and exchanged e-mails with "maybe three times." Malley, a State Department official in the Clinton White House involved in failed efforts to complete a comprehensive Israeli-Palestinian peace agreement, "is one of hundreds of people who have sent advice to the campaign," Rep. Robert Wexler (D-Fla.), an Obama supporter, wrote in the Jerusalem Post yesterday.

The persistence of the changes against Obama has left his supporters pointing fingers, both at the GOP and at the Clinton campaign. Wexler pointed to a Newsweek article this week that said Clinton senior adviser Ann Lewis had called Brzezinski Obama's "chief foreign policy adviser" during a conference call in January with leaders of major Jewish organizations. Clinton campaign spokesman Phil Singer had no comment.

And the Obama campaign released a letter to Clinton from more than two dozen Ohio Jewish leaders condemning "baseless attacks" that they said are being spread by her campaign.

Solomont referred to e-mails from the Republican Jewish Coalition, which put out a news release Monday in which Executive Director Matthew Brooks said "people should be very skeptical of Barack Obama's shaky Middle East policies."

"I have seen statements by the Republican Jewish Coalition which are distortions and misinformation, and I find it reprehensible," said Solomont, who is Jewish.

Brooks said the coalition's mailings have raised legitimate issues that voters need to scrutinize. "If you can find a distortion, have at it," Brooks said. "But those are all facts, and we think it is important to raise these issues with the Jewish community."