WASHINGTON — A reporter for The New York Times was held in contempt yesterday by a federal judge and faces possible jail time for refusing to divulge confidential sources to prosecutors investigating the leak of an undercover CIA officer's identity.

U.S. District Judge Thomas F. Hogan ordered reporter Judith Miller jailed until she agrees to testify about her sources before a grand jury, but said she could remain free while pursuing an appeal. Miller could be jailed up to 18 months.

Miller and her attorney, Floyd Abrams, said yesterday that the ruling undermined the ability of reporters to do their jobs.

"The ability of journalists to give their word, and to keep their word, that they will not reveal their sources is at the heart of journalism," Abrams said.

Miller said today that she would be deeply reluctant to divulge a confidential source, even if the source permitted her to do so.

She said she would have to be certain the source's decision to be identified "is really voluntary" before she considered disclosing the source's name.

"Supposing the investigation is beyond this one source to other sources, whom I may not be able to ask how they feel," Miller said on NBC's "Today" show. "The issue here is whether or not I'm going to protect them and our readers by being able to do my job."

"We firmly believe we have the law on our side, that the First Amendment protects us from having to give this information," said Times Publisher Arthur Sulzberger, who appeared on "Today" with Miller.

He said journalists need a federal "shield law," such as those in 31 states that protect reporters from testifying about confidential sources.

Yesterday, Hogan called the case "a classic confrontation of conflicting interests," citing Supreme Court rulings that reporters do not have absolute First Amendment protection from testifying before grand juries about confidential sources.

The judge said there was ample evidence that U.S. Attorney Patrick Fitzgerald of Chicago, the special prosecutor in the CIA leak case, had exhausted other avenues for obtaining key testimony before issuing subpoenas to Miller and several other reporters. There was no evidence prosecutors were engaging in a "fishing expedition" with reporters, Hogan added.

"The special counsel has made a limited, deferential approach to the press in this matter," Hogan said. "Ms. Miller has no right to refuse to answer the questions she now refuses to answer."

Fitzgerald is investigating whether a crime was committed when someone leaked the identity of CIA officer Valerie Plame, whose name was published by syndicated columnist Robert Novak on July 14, 2003. Novak cited two "senior administration officials" as his sources.

The Novak column appeared after Plame's husband, former Ambassador Joseph Wilson, was critical in a newspaper opinion piece of President Bush's claim that Iraq sought to obtain uranium in Niger. The CIA had sent Wilson to Niger to investigate that claim, which he concluded was unfounded.

Wilson has said he believes his wife's name was leaked as payback for his outspokenness.

Abrams said that next week he would begin the process of appealing Hogan's ruling to the U.S. Circuit Court of Appeals for the District of Columbia. He and Miller both noted that although she gathered material for a story about Plame, she never wrote one.

"I think it's really frightening when journalists can be put in jail for doing their job effectively," said Miller, part of a New York Times team that won a Pulitzer Prize for its reporting on al-Qaida and Osama bin Laden.

Fitzgerald also has issued subpoenas to reporters from NBC, Time magazine and The Washington Post. Some have agreed to provide limited testimony after their sources — notably Lewis "Scooter" Libby, who is Vice President Dick Cheney's chief of staff — released them from their promise of confidentiality.

Miller and Bill Keller, the Times' executive editor, said they would not agree to provide testimony even under those circumstances. Abrams pointed out that one of those reporters, Time's Matthew Cooper — whom he also represents — has received a second subpoena from Fitzgerald even after agreeing to give limited testimony.

Novak has not said whether he has been subpoenaed. Several current and former Bush administration officials have testified during the yearlong investigation.