A federal judge has ordered a Justice Department probe into how CBS News obtained a story two years ago disclosing an FBI investigation into a pro-Israel lobbying group, the American Israel Public Affairs Committee.

Judge Thomas Ellis III issued the order last week in connection with the prosecution of two former Aipac employees, Steven Rosen and Keith Weissman. The two men are facing criminal charges of conspiracy to acquire and disclose classified information.

Judge Ellis instructed the Justice Department “to conduct an investigation into the identity of any government employee responsible for the August 2004 disclosure to CBS News of info. related to the investigation of defendants/whether the investigation relied on info. collected pursuant to” the Foreign Intelligence Surveillance Act, according to an entry placed on the docket of the Alexandria, Va.-based court yesterday. A more detailed opinion explaining the judge’s ruling is under seal.

It is not clear whether Judge Ellis wants the alleged leak prosecuted, but disclosure of information from a foreign intelligence wiretap is punishable by up to five years in prison and a fine of up to $10,000.

On August 27, 2004, CBS reported that the FBI was about to arrest “a mole working at the highest levels of the Pentagon.” The report by Lesley Stahl on the “CBS Evening News” said the FBI had used “wiretaps, undercover surveillance, and photography, to document the passing of classified information from the mole, to the men at Aipac, and on to the Israelis.”

Ms. Stahl’s report did not cite any sources by name or organization, but CBS made several references to the thinking of “federal agents” and “investigators.”

According to court records, Messrs. Rosen and Weissman were confronted at their homes that same day and FBI agents carried out search warrants at Aipac’s offices in Washington. The timing raises the possibility that CBS learned of the probe from someone outside the government. However, it is also possible that the FBI acted after discovering that the network was about to make the investigation public.

Word of the new leak investigation met with distress from press advocates already weary from similar battles, including the jailing of a New York Times reporter in the CIA leak probe and an ongoing effort to force two San Francisco Chronicle reporters to name their sources for stories about steroid use in baseball.

“The flurry is definitely turning into a snowstorm,” the executive director of the Reporters Committee for Freedom of the Press, Lucy Dalglish, said. “This pattern is getting particularly annoying where people are covering legitimate news stories. The judge gets ticked off and orders his own investigation — that’s kind of a new twist to this.”

Ms. Dalglish said the new probe is likely to result in pressure on CBS. “Justice goes back and talks to everyone who had their hands on the FISA warrants and gets affidavits from everyone saying, ‘No. It wasn’t me,'” she said.

At that point, “The logical investigation is that you would get Lesley Stahl or her producer to identify who their confidential source is,” Ms. Dalglish said.

Ms. Stahl did not return a call seeking comment for this article. Attorneys for the government and the defense also did not respond to requests for comment on the development. Judge Ellis ordered the investigators to report back to him by September 15, but the chances of completing a serious leak probe in that time frame seem slim. An inquiry into leaks to the New York Times about planned raids on Islamic charities has been under way for five years.

The Pentagon “mole” referred to but not named by CBS in its report, Lawrence Franklin, pleaded guilty and was sentenced to 12 years in prison. He is cooperating with prosecutors.

While the outcome of the leak inquiry could be embarrassing to the government, it also poses a challenge to defense lawyers in the case, who have portrayed their clients as champions of the First Amendment and the press. It is a defense motion that prompted Judge Ellis to order the CBS probe.