The fight against terrorism would be undermined by a law to protect reporters from going to jail when they refuse to reveal their sources, the Bush administration said Wednesday.

Democrats, meanwhile, continued to pelt the White House over presidential adviser Karl Rove's (search) role in the leak of an undercover CIA officer's identity. The Senate legislation has gained attention with the recent jailing of a New York Times reporter who declined to testify in the federal investigation into the leak.

"The bill would create serious impediments to the department's ability to effectively enforce the law and fight terrorism," Deputy Attorney General James Comey said in prepared testimony to the Senate Judiciary Committee.

"It would bar the government from obtaining information about media sources — even in the most urgent of circumstances affecting the public's health or safety or national security," Comey wrote.

Sen. Christopher Dodd, D-Conn., questioned that premise. He asked opponents of the bill for examples in which shield laws in 31 states and the District of Columbia had brought about any great threats to public safety.

Legislation by Sen. Richard Lugar and Rep. Mike Pence, both Indiana Republicans, would protect reporters from being imprisoned by federal courts.

The Senate committee quickly scheduled a hearing on the proposal after a federal judge sent Times reporter Judith Miller to jail two weeks ago for refusing to divulge who told her that Valerie Plame (search), the wife of former Ambassador Joseph Wilson (search), was a CIA officer.

The bill would stop short of giving reporters absolute immunity. The sponsors added an exception for cases where source identification is essential for protecting national security.

Comey, who skipped the hearing to meet with leaders of the House on renewing the Patriot Act (search), said in his remarks that it was unfair to equate the bill with state shield laws.

"None of the states deals with classified information in the way that the federal government does," he said. "And no state is tasked with defending the nation as a whole or conducting international diplomacy."

A journalist who published Plame's identity, Matt Cooper (search) of Time, said the patchwork of state shield laws and the absence of a federal statute make it confusing for reporters promising sources anonymity in exchange for information.

"We need some clarity," he said. "I'd like to know better what promises I can legally make and which ones I can't."

New York Times columnist William Safire told the committee the bill is necessary to prevent law enforcement from turning reporters into its agents. "Journalists are not the fingers at the end of the long arm of the law," he said.

Some senators said the bill should draw a brighter line between "good leaks," whose exposure improves public life, and "bad leaks," such as the one in the Plame case, where the leak itself may have broken laws.

Sen. Chuck Schumer, D-N.Y., said "99 percent of leaks are good, and 1 percent are bad."

But Lee Levine, a media lawyer, told the committee, "One person's whistle-blower is another person's slander monger."

Democrats are demanding that President Bush fire Rove, who Cooper said gave him the first idea that the wife of Bush administration Wilson worked for the CIA.

Maintaining a Democratic drumbeat against Rove, California Sen. Barbara Boxer said the disclosure of Plame's identity was damaging to efforts by the CIA and other government agencies to attract more women.

"Karl Rove and this administration sought to destroy Wilson's wife. Now is that the way we treat women who risk their lives for their country?" she said.