CLEVELAND — Senator Obama has a solid Senate record in support of Israel.

He sings the praises, too, of Jewish civil rights workers who fought for blacks’ rights in America. And he says he wants to patch up “a historically powerful bond between the African-American and Jewish communities.”

Yet there is unease among some Jewish voters about the Illinois senator and Democratic presidential contender.

Why?

Part of it is a division between blacks and Jews that’s been growing for years, a split that Mr. Obama has challenged fellow blacks to confront.

Another element is the praise Mr. Obama has received from a Black Muslim leader, Louis Farrakhan, whose disparaging comments about Judaism are toxic to many voters. Mr. Obama’s own pastor has a history of supporting Palestinian Arab causes.

And there are questions about Obama advisers who some American Jews see as less than ardent advocates of Israel.

Finally, there are rumors and outright lies about the candidate that have gained an audience through repetition in e-mails and on Web sites.

Mr. Obama is working hard to win over this vocal, powerful and reliably Democratic voting bloc.

Jews have accounted for about 4% of Democratic primary voters so far this year, and Clinton has held a 52-46% edge over Obama among them, according to exit polls.

On the day of the Mississippi primary this week, Mr. Obama took time to call the Israeli foreign minister, Tzipi Livni, to express condolences over the deadly terrorist attack on a rabbinical seminary in Jerusalem. He also reaffirmed his support for Israel’s right to defend itself and for its commitment to negotiations with Palestinian Arabs and underscored the need to stop Iran from supporting terrorism or getting nuclear weapons.

The effort by the candidate and his advisers to calm disquiet among Jewish voters began more than a year ago.

“The Jewish community cannot be taken for granted,” one of Mr. Obama’s chief surrogates before Jewish audiences, Rep. Wexler of Florida, said. Mr. Wexler sent an e-mail last March to supporters urging them not to be swayed by rumors, a message he repeated during a recent forum in Cleveland.

Mr. Obama used a speech in January at Martin Luther King Jr.’s church in Atlanta to chastise blacks for latent anti-Semitism. And during a recent debate, Mr. Obama alluded to James Chaney, Andrew Goodman, and Michael Schwerner, one black and two Jewish civil rights workers murdered in Mississippi in 1964 as they worked together on a campaign to register black voters.

“You know, I would not be sitting here were it not for a whole host of Jewish-Americans who supported the civil rights movement and helped to ensure that justice was served in the South,” Mr. Obama said. “And that coalition has frayed over time around a whole host of issues, and part of my task in this process is making sure that those lines of communication and understanding are reopened.”

Still, there remains some “nervousness over Senator Obama” among Jewish voters, Rabbi Joshua Skoff, who attended a private meeting with Obama in Cleveland last month, said. “The rumors still have some legs.”

At the American Israel Public Affairs Committee, President Howard Friedman said Mr. Obama’s Senate record on Israel has given his critics no reason to doubt him.

But that record is thin. Just a little over three years ago, Mr. Obama was a state legislator in Illinois.

“Right now, Obama’s big problem with the Jewish community is similar to his problem with other communities: He’s just not clearly defined among any voter groups,” the director of the Center for Jewish Studies at the University of Florida-Gainesville, Kenneth Wald, said. “The fact he has a name that sounds Muslim and has a Muslim father underlines questions about what we do and what we do not know about him.”

Some critics on the Internet have gone far beyond raising questions.

Contrary to some e-mails, Mr. Obama is a Christian, not a Muslim. He took his oath of office on the family Bible, not a Quran.

“There has been a concerted effort, largely out of the conservative Web sites and anonymous e-mails,” the executive director of the National Jewish Democratic Council, which set up a Stop The Smears Web site to correct the rumors, Ira Forman, says.

“I don’t think it moves tons and tons of votes, but at the fringes, if left unchecked, it could move a few,” he said.

In the private meeting in Cleveland with 100 Jewish leaders last month, Mr. Obama talked about his 2005 trip to Israel, his views on a Palestinian Arab state and regional Middle East security. He was quickly questioned about his own pastor, the Rev. Jeremiah Wright, and an award his church magazine gave last year that said Mr. Farrakhan “truly epitomized greatness.”

Mr. Farrakhan is intolerable to Jewish voters because of a history of anti-Semitic remarks, like calling Judaism a “gutter religion.”

Mr. Obama, who has rejected support from Mr. Farrakhan, assured voters his Trinity United Church of Christ in Chicago does not endorse such messages.

“I have never heard an anti-Semitic (remark) made inside of our church. I have never heard anything that would suggest anti-Semitism on the part of the pastor,” Mr. Obama said in a transcript of his remarks released later. “He (Wright) is like an old uncle who sometimes will say things that I don’t agree with. And I suspect there are some of the people in this room who have heard relatives say some things that they don’t agree with — including, on occasion, directed at African-Americans.”

Mr. Obama took the title of his 2006 book “The Audacity of Hope” from a Wright sermon. But last year, he asked Mr. Wright not to offer a prayer at his campaign’s kickoff in Springfield, Ill.

The questioners in Cleveland also raised Mr. Obama’s use of foreign policy advisers the doubters say are foes of Israel, including the former President Carter’s national security adviser, Zbigniew Brzezinski.

Mr. Obama replied that Mr. Brzezinski is an informal, not a key, adviser, and “I do not share his views with respect to Israel.”

He said he has other foreign policy advisers from the Clinton administration who share his belief that Israel has to remain a Jewish state with special ties to America and that the Palestinian Arabs have been irresponsible. And he said critics’ e-mails never mention a member of his national finance committee, Lester Crown, who is “considered about as hawkish and tough when it comes to Israel as anybody in the country.”

“This is where I get to be honest, and I hope I’m not out of school here,” Mr. Obama told Jewish leaders at the private meeting. “I think there is a strain within the pro-Israel community that says unless you adopt an unwavering, pro-Likud approach to Israel that you’re anti-Israel, and that can’t be the measure of our friendship with Israel.”