WASHINGTON - Attorney General Alberto Gonzales insisted today that President Bush was “acting with authority” both under the Constitution and federal law in eavesdropping on Americans without warrants as part of the war on terror.

But his strong defense of Bush's program was challenged by Republican Sen. Arlen Specter, chairman of the Judiciary Committee, who told Gonzales that even the Supreme Court had ruled that “the president does not have a blank check.”

Specter suggested that the program's legality be reviewed by a special federal court.

“There are a lot of people who think you're wrong. What do you have to lose if you're right?” Specter asked Gonzales.

Gonzales initially sidestepped the question, but then said he would have no objection to such a review. He said the administration was continually looking into ways to improve the program and protect individual rights.

Gonzales, a former Texas judge, played an important role as White House counsel in developing the legal justification for the spy program. Gonzales served in the post from January 2001 to February 2005.

Sen. Patrick Leahy of Vermont, the panel's senior Democrat, said that while al-Qaida terrorists should be monitored, Bush chose to illegally wiretap Americans' conversations without safeguards to protect civil liberties.

“My concern is for peaceful Quakers who are being spied upon, and other law-abiding Americans and babies and nuns who are placed on terrorist watch lists,” Leahy said.

Gonzales told the panel that in authorizing the program, conducted by the National Security Agency, “The president is acting with authority both by the Constitution and by statute.”

Gonzales called the electronic eavesdropping program “reasonable” and “lawful.” He said published criticism of the program was often “misinformed, confused or wrong.”

Federal law “has a forceful and blanket prohibition against any electronic surveillance without a court order,” said Specter, R-Pa.

While the president claims he has the authority to order such surveillance to protect Americans from terrorist attacks, Specter said, “I am skeptical of that interpretation.”

Today's hearing into the NSA program got off to a rocky start when Democrats protested that Gonzales should be given a sworn oath before testifying.

Leahy argued that Gonzales should be sworn in like any other witness. At the very least, Gonzales should be asked if he would volunteer to being sworn in, Leahy said.

“It's not up to him,” said Specter, who was upheld by a quick party-line vote by the GOP-led committee.

Gonzales, who was not sworn in, told the committee he would voluntarily take the oath if the committee so desired. Either way, “my answers would be the same whether I was under oath or not,” he said.

Gonzales' testimony backed up comments by those defending Bush's decision to allow the NSA to eavesdrop, without first obtaining warrants, on people inside the United States whose calls or e-mails may be linked to terrorism.

He declined to discuss details of the program, as skeptics of the program have demanded. “An open discussion of the operational details of this program would put the lives of Americans at risk,” he said.

The program has sparked a heated debate about presidential powers in the war on terror since it was first disclosed in December.

Gonzales argued that Congress did, in fact, authorize the president in September 2001 to use military force in the war on terror.

He noted that the legislation “calls on the president to protect Americans both ‘at home and abroad,”' and “to take action to prevent further terrorist attacks 'against the United States.”'

Congressional Democrats have said they did not intend to order domestic surveillance when passing that measure.

Sen. Dianne Feinstein, D-Calif., told Specter last week that he should compel the Justice Department to turn over classified legal opinions on the program, using subpoenas if necessary.

The Judiciary Committee's Democrats also want Specter to call more administration officials for questioning, including former Attorney General John Ashcroft and ex-Deputy Attorney General Jim Comey, who reportedly objected to parts of the program.