WASHINGTON -- Mindful of the jailing of New York Times reporter Judith Miller, reporters are increasingly wary of pursuing stories based on confidential sources and need the protection of a federal "shield" law, a panel of journalists told the Senate Judiciary Committee yesterday.

U.S. Justice Department officials told senators, however, that they strongly oppose such a shield law, saying it is unnecessary and harmful to national security because it could prevent prosecutors from obtaining potentially vital information.

Judiciary Committee Chairman Arlen Specter, R-Pa., indicated yesterday that he doesn't accept the Justice Department argument and plans to try to win his panel's approval for a shield law later this fall. "Here you have a reporter [Ms. Miller] in jail for 85 days and millions of Americans wonder why. I'm one of those," Mr. Specter said.

Ms. Miller's case has resulted in "an obvious chilling effect on other reporters. I believe we need a statute," Mr. Specter added. Instead of relying on federal officials to decide when to try to force reporters to reveal confidential information, a federal law would leave the decision up to a judge, he said.

Currently, there is no federal shield law for reporters, although the District of Columbia and every state except Wyoming have established some type of state shield law for journalists.

Efforts to create a federal shield law have languished for years. But the issue has recently been brought into sharper public focus by Ms. Miller's case. She was released from jail Sept. 29 after receiving permission from her source, I. Lewis "Scooter" Libby, Vice President Dick Cheney's chief of staff, to reveal his name to federal prosecutors investigating the public disclosure of undercover CIA agent Valerie Plame's identity. It is a federal crime for an official knowingly to identify an undercover intelligence agent.

Under federal shield legislation sponsored by Sen. Richard Lugar, R-Ind., and Rep. Mike Pence, R-Ind., federal prosecutors would be prohibited from forcing journalists to identify sources except where "necessary to prevent imminent and actual harm to national security."

At yesterday's hearing, ABC News President David Westin testified that the lack of such legal protection in federal law for reporters means that "some information is not being told to the American people, despite the fact that the information is true and it otherwise deserves to be told.

"More than ever, our decision whether to report a story depends on more than simply whether we are confident of the truth of our story and its importance. Increasingly, we have to consider as well whether ... it's worth someone potentially going to jail," Mr. Westin said.

Ms. Miller, who was among the journalist testifying, added: "The circumstances that ... forced me to spend 85 days in the Alexandria Detention Center in Virginia highlight the urgent need for a federal shield law to protect journalists and their sources."

Chuck Rosenberg, U.S. attorney in Texas, who represented the U.S. Justice Department at the hearing, declined to discuss specifics of Ms. Miller's case. But he contended that the proposed federal shield law "could significantly interfere with the government's own legitimate investigative activities in an unnecessary and harmful way."

He added that, since a U.S. Supreme Court decision on the issue 33 years ago, the U.S. attorney general has made the final decision about whether to subpoena reporters for confidential information. Since 1991, only 12 of 243 such subpoenas have been issued, Mr. Rosenberg said.

"We seek information about confidential sources from reporters only when it really, really matters," he said. "We should not enter this debate believing that the First Amendment is under assault by the Department of Justice. Manifestly, it is not."