Judith Miller, a reporter for The New York Times, faces a jail sentence of up to 18 months for her refusal to testify in a federal investigation into who leaked the identity of an undercover CIA agent. In a brief but eloquent statement, she said, “I’m very disappointed that I’ve been found in contempt of court for an article I never wrote and The Times never published. I find it truly frightening that journalists can be put in jail for doing their jobs.”

Ms. Miller had refused to name her sources to prosecutors investigating the exposure of the agent, Valerie Plame. They want to know who told syndicated columnist Robert Novak and other journalists that Ms. Plame was a CIA official. Mr. Novak included that information in his newspaper column. Ms. Miller published no articles about the agent. But U.S. District Judge Thomas F. Hogan found her in contempt of court and ordered her jailed. He noted that she had contemplated writing such an article and had conducted interviews for it. He said she was mistaken in believing that reporters have a First Amendment privilege that overrides the government’s right to inquire into her confidential sources. He suspended his jail order pending Ms. Miller’s appeal.

The case raises serious questions about the news reporting business and the use of confidential sources. Arthur Sulzberger Jr., publisher of The Times, called Judge Hogan’s order “an attack on the ability of all journalists to report on the actions of governments, corporations and others.” He said the protection of confidential sources had been critically important in uncovering the Watergate scandal, health-threatening practices of the tobacco industry and police corruption. He could have added that secret intelligence reports about the war in Iraq came to light because outraged government officials told reporters about them in “deep background” interviews.

Another quirk in the case is that the prosecutors relied on secret filings to explain why Ms. Miller’s testimony is required. Judge Hogan refused to release even a summary of the filings to her or her lawyer.

Now, no one likes news stories based on undisclosed sources. But news organizations generally accept the practice as a protection for whistle blowers, and a means of getting officials to discuss matters frankly without following official “talking points.” The public is the beneficiary.

In a new technique to persuade reporters to testify, the prosecutors asked officials suspected of disclosing Ms. Plame’s identity to sign waivers absolving reporters from their confidentiality agreements.

Other reporters, including Tim Russert of NBC, Walter Pincus and Glenn Kessler of The Washington Post, agreed to testify, saying that they relied on direct assurances from their sources or their lawyers that they were free to reveal confidential conversations. That was not good enough for Ms. Miller. Officials who signed the waivers may have done so because they feared that refusing would cast suspicion on them or endanger their jobs, said The Times’ executive editor, Bill Keller.

Ms. Miller was right, and the other reporters were wrong in going along with a practice that could break down a confidentiality system that, despite its flaws, helps get information to the public about what is really going on in government, industry, and our society as a whole.