The case represents the starkest confrontation between the press and the government since 1971, when the Supreme Court refused to stop The Times and The Washington Post from publishing a classified history of the Vietnam War known as the Pentagon Papers. And legal experts said yesterday that they knew of no other instance in modern journalistic history in which a major news organization announced that it would disclose the identities of its confidential sources in response to a government subpoena.

The press has traditionally argued that it needs to be able to protect confidential sources to ensure that the public is fully informed. Some courts have recently rejected that position outright. Other have said that the interest in the flow of information to the public in given cases was outweighed by the needs of the judicial system for evidence.

On Wednesday, Judge Thomas F. Hogan of Federal District Court in Washington said he would order the reporters jailed for up to 120 days if they did not agree to testify before the grand jury in the meantime. He also said he would impose substantial fines on the magazine.

The magazine made its decision over the objections of its reporter.

"For almost two years," Mr. Cooper said yesterday, "I've protected my confidential sources even under the threat of jail. So while I understand Time's decision to turn over papers that identify my sources, I'm obviously disappointed by what they chose."

The documents to be turned over to the special prosecutor in the case, Patrick J. Fitzgerald, include Mr. Cooper's notes of interviews and "the ordinary work product that is typical of the interaction that takes place between reporters and editors," Mr. Pearlstine said. He said Time had not decided how the transfer would happen but said the documents would not be made public by Time.