In a dispute that commingles foreign policy and a quest for political advantage, U.S.-Israel relations have taken an unexpectedly central role in the California race for Senate.

Rivals in the race for the Republican nomination are questioning whether former Rep. Tom Campbell is sufficiently supportive of Israel. They base their criticisms on his voting record, statements about a Palestinian homeland and capital, and some of his past associates.

Their allegations have raised enough concerns for Campbell that he plans to meet Monday with the influential American Israel Public Affairs Committee. He also is reaching out to other Jewish leaders. His campaign's honorary chairman, former U.S. Secretary of State George P. Shultz, weighed in to call Campbell's support for the nation "unwavering."

"He clearly understands the very real threats facing the Israeli people, all the more urgent now as Iran rushes toward nuclear arms," Shultz said in a statement released to The Times. "Tom Campbell's record of action tells you where he stands, and I stand with him."

The two other major Republican primary contestants, former businesswoman Carly Fiorina and Orange County Assemblyman Chuck DeVore, have launched criticisms of Campbell. The rhetoric has grown so heated that a prominent supporter of Campbell's has accused Fiorina's campaign manager of calling Campbell an "anti-Semite." The campaign manager denies the accusation.

The debate over Campbell's Israel credentials, which has been roiling on Jewish and conservative websites, is a rare one in American politics, and even less frequent in Republican primaries compared with Democratic competitions, said Dan Schnur, director of the Jesse M. Unruh Institute of Politics at USC and a former GOP political operative.

"Support for Israel is a pretty universal concept among Republicans," he said. "Support for Israel is a pretty broad-based concept in American politics."

But more than foreign policy appeared to be at play. Evangelical Christians have a strong affinity for the state of Israel, for political reasons and because they say support for it is emphasized in the Bible. For years surveys have shown evangelical support for Israel far outweighs that of the general population -- and evangelicals are a key bloc among Republican primary voters.

"The bigger concern for Campbell is less with Jewish voters than with religious conservatives," Schnur said.

The issue has sparked at least one dispute among prominent Republicans. Former California Secretary of State Bruce McPherson said in an interview that when he called Fiorina manager Marty Wilson to tell Wilson he planned to endorse Campbell, Wilson replied, "Bruce, how can you do that? He's an anti-Semite."

McPherson, who said he would have endorsed Fiorina if Campbell wasn't in the race, said he was stunned. He and Campbell have known each other for more than two decades, he said, and Campbell has never given any such indication.

"As a matter of fact, I know he's a strong supporter of the state of Israel," McPherson said.

Wilson denied making the comment. "That's not true, absolutely not," he said, adding that he does not believe Campbell is anti-Semitic. "That's crazy."

Wilson said he discussed the endorsement with McPherson but did not recall discussing Israel.

"It's uncharacteristic of Bruce to sit there and make that kind of a claim," Wilson said, adding that he had known McPherson for years.

Criticism of Campbell's voting record centers on efforts to reduce foreign aid for Israel. While in Congress, Campbell said, he supported military aid for Israel but twice sought to reduce economic aid. In the late 1990s, when foreign aid to other nations was being cut to help balance the budget, Israel's allocation was not affected. Campbell said he favored allowing the military aid to remain unchanged but supported slightly reducing economic aid.

A second instance occurred when he voted against giving Israel an additional $30 million in economic aid, which was to have been taken from funds set aside for the neediest nations, such as those in Africa. That money, he said, was on top of a $700-million aid request that he supported and an earlier $3-billion appropriation.

Campbell noted that he has traveled to various African nations to teach and has seen first-hand how much difference even a small amount of money could accomplish.

"I remember the mayor of a village in northern Malawi came out to thank us for a little water pump. It was probably under $50, and it allowed the water from the river to be brought to this area," Campbell said. "You don't forget things like that."

Campbell also drew criticism in the past for saying that Jerusalem should be the shared capital of both Israel and a Palestinian state. He said in the interview that he stands by that view.

His opponents also questioned Campbell's past associates, notably Sami Al-Arian, a former University of South Florida professor who pleaded guilty in 2006 to conspiring to help a terrorist organization. Al-Arian had donated $1,300 to Campbell's 2000 campaign for Senate. Campbell, who was the business school dean at UC Berkeley and now teaches at Chapman University, wrote a letter to the University of South Florida protesting its decision to fire Al-Arian over comments he made. He also visited Al-Arian's brother in jail.

Campbell said he did not know about Al-Arian's illegal activities at the time and said that if he had he would not have written the letter.

"None of that had come out," he said. Al-Arian was also photographed with George W. Bush during his first presidential campaign, Campbell noted.

Jewish leaders expressed confidence that Campbell is not anti-Semitic, but said he was not regarded as a "friend of Israel."

"He's a brilliant gentlemen and an engaging personality, and I don't think he's particularly pro-Israel," said Rabbi Abraham Cooper, the associate dean of the Simon Wiesenthal Center in Los Angeles, who has known Campbell since the 1980s. "I think there's enough there on the record that would send real alarms that this is someone who maybe doesn't fully understand, doesn't fully value or fully support a strong ongoing relationship with the state of Israel, an alliance with the state of Israel."

Campbell called his opponents' efforts to undermine his Israel record "unacceptable," and singled out Wilson's alleged comment to McPherson as "reckless and irresponsible."

"It's also personally hurtful," he added.