The prosecutor in the CIA leak case said yesterday that he plans to present evidence to another federal grand jury, signaling a new and potentially significant turn in the investigation into the unmasking of CIA operative Valerie Plame.

Three weeks after indicting I. Lewis "Scooter" Libby and declaring the investigation nearly complete, Special Counsel Patrick J. Fitzgerald announced a new phase in the investigation after the disclosure this week that a senior administration official revealed Plame's CIA connection to Washington Post Assistant Managing Editor Bob Woodward in mid-June 2003.

Legal experts said Fitzgerald's decision to call upon a new grand jury is all but certainly because he is considering additional criminal charges in the case.

Two sources close to Karl Rove, the top Bush aide still under investigation in the case, said they have reason to believe Fitzgerald does not anticipate presenting additional evidence against the White House deputy chief of staff. Instead, lawyers involved in the case expect the prosecutor to focus on Woodward's admission that an official other than Libby told him about Plame one month before her identity was publicly disclosed in a July 14, 2003, column by Robert D. Novak.

Woodward, who was questioned by Fitzgerald on Monday, has refused to reveal the source's name publicly, but a person familiar with the investigation said the source had testified earlier in the case. The source came forward to the prosecutor again after Woodward started asking questions for an article on the CIA leak late last month and reminded the person of their 2003 conversation, Woodward said yesterday. That raises the possibility that the source faces legal problems if he or she provided false or incomplete information during previous testimony, according to legal experts.

Fitzgerald's decision to present information to a new grand jury, contained in a court filing and announced publicly at a court hearing on the Libby case yesterday, is the latest twist in an investigation that has rattled the White House and threatens top administration officials. "The investigation will involve proceedings before a different grand jury" from the one that indicted Libby, Vice President Cheney's former chief of staff, on perjury and obstruction-of-justice charges, Fitzgerald said. "The investigation is continuing."

The most innocuous explanation for the new grand jury is that Fitzgerald simply wants to complete his probe and to put information on the record, perhaps about Woodward's source or Rove, according to several legal experts, including some involved in the case.

But most lawyers interviewed for this article said Fitzgerald would not go through the trouble of calling upon a new grand jury -- after gathering so much testimony from and about Rove -- unless he is exploring new territory uncovered since the Oct. 28 Libby indictment.

"Whoever's Woodward's source probably feels terribly uncomfortable right now," said E. Lawrence Barcella Jr., a Washington defense lawyer and former prosecutor.

Randall D. Eliason, a law professor who formerly ran the public corruption section of the U.S. attorney's office in Washington, said Fitzgerald is clearly "looking at new defendants or new charges." That is not good news for anybody concerned about their role in Plame's identity being leaked, Eliason added.

For nearly two years, Fitzgerald has been investigating whether senior Bush administration officials illegally leaked classified information -- Plame's identity as a CIA operative -- to the news media to discredit allegations made by her husband, former ambassador Joseph C. Wilson IV. Plame's name was revealed in Novak's column eight days after Wilson publicly accused the administration of twisting intelligence to justify the Iraq war.

Libby, who was forced to resign from Cheney's office, was charged with committing perjury, providing false statements and obstructing justice and has denied wrongdoing. Libby's attorneys have called Woodward's disclosure a "bombshell" that could bolster Libby's defense.

In anticipation of a lengthy and expensive court fight, a number of Republican former senators, former ambassadors and fundraisers are planning to raise $250,000 each and a total of $5 million for Libby's legal fund, according to people familiar with the plan. In a private conversation earlier this week, Republicans such as former ambassadors Melvin Sembler and Howard Leach promised to raise at least $250,000. Former senators Fred D. Thompson (Tenn.) and Alan K. Simpson (Wyo.) and former congressman Bill Paxon (R-N.Y.) are also part of the fundraising campaign, the sources said.

"Good lawyers are expensive," said Barbara Comstock, a spokeswoman for the Libby legal team. A few Democrats, including R. James Woolsey, a former CIA director, are also involved.

At the very least, Woodward's disclosure has put the spotlight on someone other than Libby for the moment. In his deposition, Woodward testified that he spoke with Libby twice in late June 2003 and does not recall Libby raising the subject of Plame. Woodward said it is possible he mentioned Plame to Libby because he had included her name on a list of questions he planned to ask, but he testified that he does not recall doing so, according to a statement he released on Tuesday.

Experts said that Fitzgerald is not trying to shore up his case on Libby. Under court rules, Fitzgerald cannot use a new grand jury to gather additional evidence for an indictment he has already brought, or to wrap up unanswered questions in preparation for Libby's trial. He can only call on a grand jury to hear evidence if he is considering new charges against another person or additional charges against Libby.

One mystery for the public -- but not for Fitzgerald -- is the identity of Woodward's source. Woodward said he contacted the source late last month for an article on the CIA leak case and discussed notes showing that the source had mentioned Plame in mid-June 2003. The source then went to Fitzgerald.

The source's situation appears not unlike Rove's. In his initial testimony, Rove did not reveal his conversation about Plame with Time magazine's Matthew Cooper. Only after an e-mail surfaced showing that Rove had discussed the issue with Cooper did the top Bush aide tell the grand jury about it. Sources close to Rove said he is under investigation for possibly providing misleading statements about the Cooper conversation.

Lawyers in the case say Woodward's source must not have initially mentioned the 2003 contact with him and told Fitzgerald about it only after talking to Woodward last month.

"None of this would be a news flash if this person had previously been interviewed or testified and had previously disclosed this information to investigators," Barcella said. "You have to assume they didn't disclose this interview with Woodward. Now the prosecutor has to investigate why they didn't."

Barcella said it may be difficult for the source to claim he did not recall talking to Woodward. "But, really, could anybody forget a conversation with the icon?" he asked.

At yesterday's hearing, U.S. District Judge Reggie B. Walton told Libby's attorneys that he had read their recent comments about the Woodward matter in media accounts and urged them to hold their tongues until the trial, to avoid prejudicing future jurors. He said he has never issued a gag order in a case and hopes not to have to do so.

"I do have a very strong proclivity on cases being decided based on evidence presented in trial . . . not in the press," he said. "I assume . . . a word to the wise to be sufficient."

At the hearing, Fitzgerald reached a compromise with Dow Jones and Co. and the Associated Press to ensure that some evidence gathered in the Libby prosecution could be revealed publicly. The two sides agreed that classified material, private personal information and secret grand jury testimony will be kept secret from the public and the news media, but that other information can be revealed in court filings.

Patrick J. Fitzgerald said he plans to present new evidence to a grand jury.