The prosecution of two pro-Israel lobbyists charged with obtaining and distributing classified information is looking shakier after two former American ambassadors to Israel and two officials who once oversaw security classification policy for the federal government agreed to testify for the defense.

A former executive editor of the New York Times, Max Frankel, and the State Department’s top intelligence official from 2001 to 2003, Carl Ford Jr., are also among the expert witnesses identified on Friday in court filings by lawyers for the former employees of the American Israel Public Affairs Committee, Steven Rosen and Keith Weissman.

The two classification experts on the defense witness list, Steven Garfinkel and J. William Leonard, headed the federal government’s Information Security Oversight Office from 1980 through last year.

“They are the voice of the official consensus on classified information. If they are siding with the defense, then that’s devastating to the prosecution,” a leading authority on and critic of federal classification policy, Steven Aftergood of the Federation of American Scientists, said. “If you have Garfinkel and Leonard, who have covered this for the last three decades over five administrations, and they are critical of the classification claim, that’s a serious problem for the prosecution.”

Messrs. Rosen and Weissman were indicted in 2005 on charges that they conspired with a Pentagon official, Lawrence Franklin, to relay classified information to journalists and foreign officials. The indictment obscures some key details, but some of the information was reportedly relayed to Israeli diplomats and included details of Iranian involvement in Iraq.

Franklin pleaded guilty and was sentenced to more than 12 years in prison. He is now cooperating with prosecutors and is expected to seek a sentence reduction.

The case against Messrs. Rosen and Weissman has drawn protests from journalism groups and First Amendment advocates who say it could open the doors to prosecution of reporters who routinely seek, obtain, and disclose classified information in ways not dissimilar from that of the two lobbyists. However, Judge Thomas Ellis III rejected the defense’s attempt to toss out the case on constitutional grounds.

“This is a very interesting case to a lot of people in the executive branch and, I assume, in the press as well,” one potential expert for the defense, who asked not to be named, said yesterday. “It seems like an overreach.”

Messrs. Rosen and Weissman are scheduled for trial on April 29, but the trial date has already slipped repeatedly and is likely to do so again, particularly if the Justice Department appeals Judge Ellis’s rulings about how classified information may be presented.

Sources told The New York Sun that at least some listed defense witnesses were given access to key records about the case, a development that suggests they endorse the defense’s view that the prosecution is unwarranted. However, a lawyer for Mr. Weissman, John Nassikas, said yesterday that the expert witnesses were chosen to address specific issues regarding classification and diplomatic practice. “The average expert here is going to be hitting on flaws in the government’s case, not saying there was a miscarriage of justice,” the defense attorney said.

There is no guarantee that the proposed experts will testify. Next week, the prosecution and defense are expected to file motions objecting to some or all of the witnesses.

The former ambassadors to Israel who have agreed to testify for the defense are Samuel Lewis, who served from 1977 to 1985, and Edward Walker Jr., who served from 1997 to 2000. Also on the list is a former American ambassador to Turkey and deputy chief of mission in Tel Aviv, Mark Parris.

At trial, prosecutors may try to undermine some of the witnesses by suggesting they have an affinity for Aipac. Messrs. Lewis and Parris, for instance, served as counselors at a think tank that shares donors and board members with Aipac, the Washington Institute for Near East Policy. However, Mr. Walker headed a pro-Arab think tank, the Middle East Institute. In 2001, he complained to the Jordan Times that Washington was in the thrall of “the very committed supporters of the Israeli right.”

Another defense expert, Morton Halperin, served in national security-related jobs in the Johnson, Nixon, and Clinton administrations, but is presently director of American advocacy for the Open Society Institute, a liberal group funded by a billionaire financier, George Soros. “Mort Halperin is far from being a patsy for Aipac. He’s a critic of U.S. policy in the Mideast,” Mr. Aftergood said.

In November, Judge Ellis approved a defense request to subpoena 15 current and former American officials as so-called fact witnesses. They include President Bush’s national security adviser, Stephen Hadley; Secretary of State Rice; a former deputy secretary of state, Richard Armitage, and two former Defense Department officials, Douglas Feith and Paul Wolfowitz.

The new list of potential defense experts was first reported by the Jewish Telegraphic Agency.