The No. 2 official at the Justice Department said Wednesday that a shield law for reporters would encourage leaks of classified information.

At a Senate Judiciary Committee hearing, Deputy Attorney General Paul McNulty also said the proposal to protect reporters from having to identify their sources would "significantly weaken" the department's ability to obtain information it needs to protect national security.

Senate Judiciary Committee Chairman Arlen Specter, R-Pa., rejected McNulty's opposition, saying he wants to push forward with the bill, inspired in part by last year's jailing of journalist Judith Miller, then of The New York Times.

Miller had refused to cooperate with prosecutors in the Valerie Plame leak investigation. She subsequently disclosed that the source who told her of Plame's CIA identity had been Vice President Dick Cheney's now-indicted former chief of staff, I. Lewis "Scooter" Libby.

The Senate proposal would allow reporters to protect their confidential sources only in some instances. There would be exemptions in cases involving guilt or innocence, death or bodily harm, eyewitness accounts of criminal activity, and unauthorized disclosure of properly classified information.

McNulty said an exemption for national security was inadequate because the government would have to prove in court that a news leak harmed security. The Senate legislation would inject the federal judiciary "to an extraordinary degree" into executive branch functions, said McNulty.

A former solicitor general in the Bush administration, Theodore Olson, supported a shield law, saying it would promote investigative journalism.

"Naturally, the Department of Justice does not want its judgments second-guessed by courts," Olson testified. But Congress should not recoil from ensuring judicial oversight on government decisions such as warrants for eavesdropping on phone conversations, Olson said.

Clarity also is needed given a split in the federal courts as to whether journalists are entitled to protections, Olson added.

In an interview, Lucy Dalglish, executive director of the Reporters Committee for Freedom of the Press, said it was frustrating listening to testimony about "false, overwrought warnings about national security."

The 109th Congress is running out of time to act on the legislation. A House version of the bill would allow courts to compel reporters' testimony when necessary to prevent "imminent and actual harm" to national security. Differences between the two bills would have to be reconciled in a conference committee after the two chambers pass the bill.