WASHINGTON – A federal judge yesterday sent a New York Times reporter to jail for refusing to identify her sources to a grand jury investigating the leak of a CIA operative’s identity, while a Time magazine reporter subpoenaed in the same inquiry won a last-minute reprieve after his source apparently relinquished any claim of confidentiality.

Judge Thomas Hogan ordered that the Times reporter, Judith Miller, be incarcerated until the grand jury expires in late October, or until she agrees to testify.

“The court has to take some action to attempt to get her to comply. I can’t tell whether it will be successful or not,” the judge said sternly during an afternoon hearing. “It may be that the confinement will convince her.”

Ms. Miller’s lawyer, Robert Bennett, asked Judge Hogan to release her or place her under house arrest, but the prosecutor, Patrick Fitzgerald, said that would set a bad precedent. “You cannot make history by having this case stand for the proposition that the law and this court don’t count,” he said.

Judge Hogan said giving Ms. Miller “a pass” would embolden others to defy the courts. In that event, the judge said, “we are on a very slippery slope and will descend into anarchy.”

Turning aside another request from Ms. Miller’s attorneys, Judge Hogan ordered the veteran national security and foreign correspondent taken into custody immediately. She embraced her lawyers and was led out of the courtroom by two federal marshals.

Before being ordered to jail, Ms. Miller told the judge that she felt compelled to keep her sources secret and viewed her defiance as an act of “civil disobedience.” “If journalists cannot be trusted to guarantee confidentiality, then journalists cannot function and there cannot be a free press,” she said.

Mr. Bennett called the situation a “tragedy,” but the judge disagreed.

“I don’t understand how it’s a tragedy. It’s Ms. Miller’s decision to do this,” he said.

For Time magazine’s Matthew Cooper, it was a bewildering day that he said he began by sending his 6-year-old son to summer camp with the news that his father would be gone for a while. A short time later, the Time reporter told the court, he was contacted “in a somewhat dramatic fashion” by his source, who offered “express personal consent” for Mr. Cooper to testify about the confidential conversations. The unexpected development effectively lifted the threat of jail for Mr. Cooper.

The investigation that enmeshed the two journalists stems from a July 2003 op-ed piece in which a former American diplomat, Joseph Wilson IV, disputed President Bush’s statements about Iraq’s efforts to obtain nuclear materials. Within days of the publication of Mr. Wilson’s piece, accounts began to appear in the press identifying his wife, Valerie Plame, as a CIA employee and suggesting that she had arranged for her husband to undertake an official mission to Africa to assess some of the reports about Iraqi nuclear procurement there.

The deliberate disclosure of a covert agent’s identity by a government official can be a violation of federal law. Mr. Wilson has accused Bush administration officials of seeking to smear him for his criticism of the president.

In an effort to locate the leakers, an unknown number of executive-branch officials were asked to execute boilerplate waivers, releasing any journalists they might have spoken with from promises of confidentiality. Judge Hogan appeared to credit the waivers, but Mr. Cooper and Ms. Miller said they were meaningless.

“These government-issued waivers that the prosecutor has been handing out are not worth the paper they’re written on,” Mr. Cooper said.

Mr. Fitzgerald dismissed concerns that the waivers were coerced. “We don’t control who gets fired and who doesn’t,” he said.

Mr. Cooper declined to publicly identify the source who contacted him yesterday. However, Newsweek reported recently that the Time correspondent’s notes indicate he spoke with the president’s top political adviser, Karl Rove, a few days before Ms. Plame’s identity was disclosed.

In an interview, Mr. Rove’s attorney, Donald Luskin, declined to discuss whether his client is the one who released Mr. Cooper from his promise yesterday. Mr. Luskin called the Newsweek account “70% wrong” and said he confirmed only that Mr. Cooper called Mr. Rove during the week in question. “I state categorically that my client did not disclose Valerie Plame’s identity to Matt Cooper or anyone else,” Mr. Luskin said.

Time magazine’s decision last week to turn over Mr. Cooper’s e-mails and some notes may have led the source to conclude that there was little purpose in having the Time journalist go to jail.

Mr. Bennett said he suspects the investigation will come to naught. “I have the nagging feeling, the nagging feeling that Judy Miller may be the only person to go to jail in this case,” he said.

Judge Hogan described as untenable Ms. Miller’s assertion that her sources had to remain confidential under any circumstances. He cited the 1975 assassination of the CIA’s station chief in Greece, Richard Welch, after he was exposed by a former CIA agent, Philip Agee. The judge said that Ms. Miller’s views would also compel her silence, even if a murder were involved.

A somber Mr. Cooper said after the hearing that as Ms. Miller was sent away he urged her to “stay strong.” He said he hopes the present standoff will give an added push to efforts to enact a federal shield law that could protect reporters from having to testify. However, the proposed legislation, similar to laws already on the books in many states, is not absolute. Many legal experts, including judges who have ruled on the current dispute, have said Ms. Miller and Mr. Cooper would likely have been forced to testify even if Congress or the federal courts granted journalists special protection.

The judge’s references yesterday to Ms. Miller’s actions as akin to obstruction of justice, and the prosecutor’s pointed note in a recent court filing that the reporter’s defiance was a “crime,” raised the prospect that Ms. Miller could be charged with criminal contempt.

“The government has it within its power to do that,” an attorney for Ms. Miller, Floyd Abrams, said in response to a reporter’s question. “If Mr. Fitzgerald wants to take that additional step of criminalizing this, making the clash between the government and the press even worse, even more egregious, even more confrontational, he can do that.”

Yesterday’s government-press showdown spawned protests in Washington and elsewhere. Just prior to the hearing, free-press advocates gathered in a park near the courthouse to rally for the pending legislation that would create a reporter’s privilege in the federal courts. Reporters supporting Ms. Miller also demonstrated outside the New York Times headquarters in Manhattan.