WASHINGTON — Two days after seemingly locking up the Democratic nomination for president with impressive performances in North Carolina and Indiana, Sen. Barack Obama took time out from courting party leaders to speak at a 60th birthday celebration for Israel at the gilded, classical Andrew W. Mellon Auditorium.

Stepping up to a microphone, flanked by Israeli and American flags, Obama sounded notes carefully tailored to the crowd of 1,200. With a practiced deftness, he praised Zionist leaders Theodor Herzl and David Ben-Gurion, cited the Holocaust and recalled an Israeli helicopter ride that reaffirmed for him "the dangers faced by this particularly narrow strip of land."

Obama was rewarded with several ovations and a hug from Israeli Ambassador Sallai Meridor.

But the event could not entirely mask the fact that doubts remain about the Illinois senator among some quarters of the Jewish community, where uncertainty lingers about his commitment to Israel and issues such as his relationship with Rev. Jeremiah Wright Jr., which one New York legislator said "scares me very, very much."

Jewish voters are near the top of the list of voting blocs Obama will have to reach out to as he turns to the general election. From appearances in synagogues to meetings with Jewish groups and even an interview with an Israeli newspaper, Obama's courtship shows some signs of paying off, with a recent Gallup Poll suggesting Obama leading Sen. John McCain 61 percent to 32 percent among Jewish voters.

As Obama closes in on the Democratic nomination, Republicans are stepping up their attacks on Israel-related issues, with McCain and House Republican leader John Boehner of Ohio taking swipes recently, and President George W. Bush assailing "appeasement" Thursday in a Jerusalem speech that many saw as a shot at Obama. Obama's campaign has responded furiously; the senator already was engaged in an aggressive outreach campaign to Jewish voters, including a three-day trip to Florida to begin Wednesday.

Still, Obama's lead among Jewish voters is a smaller margin than other Democratic nominees have enjoyed. And doubts about Obama's stands on Jewish issues and Israel stubbornly persist in segments of the community, in part due to methodical campaigns against him by his conservative critics.

"Barack is an extremely intelligent person, but you can't go dancing around here," said Illinois state Sen. Ira Silverstein, an Orthodox Jew who once shared an office with Obama and wants more specifics on Middle East policies. "People come to me wanting answers, and I try to do my best. He has some more work to do."

Jews make up less than 2 percent of the U.S. population, but they are well-organized, politically active and concentrated in a handful of key states, including classic swing states such as New Jersey and Florida. In some ways, Obama would seem a natural fit for the Jewish community, which is disproportionately Democratic, liberal and pro-civil rights. And many Jews have indeed been quick to embrace Obama.

But others have raised questions. "Since we don't have a lifetime of experience with him, we need to know who he is, this man who has suddenly come on the scene, who is very exciting, a good speaker and handles himself beautifully," said New York Assemblyman Dov Hikind. "We don't want to be fooled by these things that at the end of the day don't matter that much."

Rep. Robert Wexler (D-Fla.), an ardent Obama supporter, said such questions have good answers. "His record on Israel is an A-plus," said Wexler, who represents more Jews than any other congressman. "His support for Israel's right to self-defense is perfect. He was supportive of Israel's right to build a security fence. He stood steadfast with Israel in its fight with Hamas. Having said that, there is an unfamiliarity, and we're having an aggressive outreach program. There are questions, no doubt. But I think we are answering them."

Among the concerns for some is Obama's professed willingness to talk with dictators, presumably including enemies of Israel like Iran's Mahmoud Ahmadinejad. Some have complained that Obama is getting foreign policy advice from experts such as Robert Malley and Zbigniew Brzezinski, who are seen as less friendly to Israel, though Obama's campaign says the two are merely among hundreds of people who have offered counsel. Earlier this month, Malley severed his ties to the Obama campaign.

More broadly, some Jews, fairly or not, are doubtless uneasy with Obama's connections to the Muslim world. Some of his family members were Muslim, he lived in Indonesia as a child, and he has befriended such controversial figures as Palestinian activist Rashid Khalidi.

"He speaks with extraordinarily empty platitudes about the Middle East," said Herbert London, president of the conservative Hudson Institute, who is Jewish. Of Obama's openness to talking with dictators, London is contemptuous: "That is almost child's play. It is adolescent talk you might hear from a 14-year-old."

There have long been tensions between the Jewish and African-American communities, and those were exacerbated by the emergence of Wright, Obama's pastor. "There's this relationship with a guy who said 'Zionism is racism'—that is anti-Semitism," said Abraham Foxman, national director of the Anti-Defamation League of B'nai B'rith.
The questions about Obama, however, did not arise only organically. A series of anonymous e-mails targeted at Jews suggested Obama was secretly a Muslim, took oaths on the Quran and attended an Islamic religious school—all false, and all infuriating to Obama's Jewish supporters.

"There is an organized effort to discredit Sen. Obama in the Jewish community that is more relentless and aggressive than anything I've ever seen," said Alan Solomont, a major Obama supporter and fundraiser in Boston. "It starts probably among the far-right-wing neocons, bloggers, Bush supporters in the Jewish community who see Sen. Obama as an easy target to exploit in the Jewish community."

It's not just bloggers seeking to drive a wedge between Jews and Obama. The Republican Jewish Coalition has sent out a series of statements blasting Obama's positions on Israel. The Tennessee Republican Party issued a press release headlined "Anti-Semites for Obama" after Louis Farrakhan endorsed him in February, an endorsement the Illinois senator rejected.

Now national GOP leaders seem to be taking up the cause more openly. McCain recently highlighted a Hamas official's comment that he would welcome an Obama presidency. House Minority Leader Boehner accused Obama of calling Israel a "sore" on American's foreign policy, a somewhat brazen misrepresentation of Obama's comments in a May 12 interview.

With all this, Obama has received significant Jewish support in the Democratic primaries. In Pennsylvania, Sen. Hillary Clinton outpolled Obama 62 percent to 38 percent among Jews, but in Massachusetts he edged her 52 percent to 48 percent. In a recent nationwide Gallup Poll, Jewish voters preferred Clinton to Obama 50 percent to 43 percent, a notable but hardly overwhelming margin.