The Justice Department has threatened to file criminal charges against a former top National Archives official if he testifies as a defense witness in a high-profile national-security case.

J. William Leonard, who resigned last January as the U.S. government's chief expert on classified information, after a bitter clash with Vice President Dick Cheney's office, has been cooperating with defense lawyers in a case charging two former officials of the American Israel Public Affairs Committee (AIPAC) with improperly disclosing national-security secrets, according to recently filed court papers.

The threat to file charges against Leonard—for allegedly violating federal ethics laws—was laid out by prosecutors in a public-court filing last spring, but got no public attention. In recent weeks, however, it has become the latest point of contention in a case that has generated enormous controversy in foreign-policy and civil-liberties circles.

The case charges that Steven Rosen, the former chief foreign policy aide at AIPAC, and Keith Weissman, the group's former chief Iran analyst, violated a World War I-era law, called the Espionage Act, when they allegedly passed along national security secrets to officials at the Israeli Embassy and to reporters. They had learned the alleged secrets in meetings with high-level government officials, including then national-security adviser and now secretary of State, Condoleezza Rice. The two men are the first nongovernment officials ever to be prosecuted for disseminating "national defense information" under the law, raising concerns that others—including members of the news media—could ultimately face similar kinds of charges if the government's case is successful.

But the secret information Weissman and Rosen are being accused of passing along might not have been secret at all. Lawyers in the case told NEWSWEEK that, after reviewing a large volume of sealed evidence, Leonard was prepared to testify that the information at issue was either not properly classified or was already available from public sources, including newspaper accounts.

"This is a bizarre twist," said Steve Aftergood, a national security specialist for the Federation of American Scientists, who has followed the case closely.  "If [Leonard] is right, not only are the defendants innocent, there was no crime."