SAN ANTONIO -Present Bush strongly defended his domestic spying program on Sunday, calling it legal as well as vital to thwarting terrorist attacks, and contended the leak making it public had caused "great harm to the nation."

"This is a limited program designed to prevent attacks on the United States of America and, I repeat, limited," Bush told reporters after visiting wounded troops at Brooke Army Medical Center. "I think most Americans understand the need to find out what the enemy's thinking."

In Washington, lawmakers are preparing for hearings to consider Bush's domestic spying program.

Four senators — two of them Republicans — indicated Sunday that congressional hearings were appropriate for considering Bush's assertion that he had constitutional and congressional authority to authorize domestic wiretaps without a court order in the aftermath of the terrorist attacks of Sept. 11, 2001.

"In the first few weeks we made many concessions in the Congress because we were at war and we were under attack," said Sen. Richard Lugar (news, bio, voting record), R-Ind., the chairman of the Foreign Relations Committee. "We still have the possibility of that going on, so we don't want to obviate all of this. But I think we want to see what, in the course of time, really works best."

The New York Times reported last month that the National Security Agency had been conducting warrantless surveillance since 2002. Bush then acknowledged that he had authorized the NSA program and pointed to informing congressional leaders and regular reviews by administration officials as evidence of oversight for the program.

The Justice Department on Friday opened an investigation into the leak that resulted in news stories about the secret order to eavesdrop on Americans with suspected ties to terrorists.

"The fact that somebody leaked this program causes great harm to the United States," Bush said before returning to Washington from a holiday break at his Texas ranch. "There's an enemy out there."

Bush stressed that the surveillance involved telephone calls from "a few numbers" outside the United States by people associated with al-Qaida, the terrorist organization that plotted the Sept. 11 attacks. The White House later clarified Bush's remarks, saying he meant to say calls going to and originating from the U.S. were being monitored.

"It seems logical to me that if we know there's a phone number associated with al-Qaida or an al-Qaida affiliate and they're making phone calls, it makes sense to find out why," he said. "They attacked us before, they'll attack us again."

Bush didn't answer a reporter's question about whether he was aware of any resistance to the program at high levels of his administration and how that might have influenced his decision to approve it.

The Times reported Sunday that a top Justice Department official objected in 2004 to aspects of the NSA program and would not sign off on its continued use as required by the administration's guidelines.

James B. Comey, a top deputy to then-Attorney General John Ashcroft, was concerned with the program's legality and oversight, the Times and Newsweek reported. Administration officials then went to Ashcroft, who had been hospitalized for gallbladder surgery, to gain his approval, according to the newspaper, but it was unclear whether Ashcroft gave his approval.

Neither Comey nor Ashcroft would comment on the meeting, according to the Times. White House spokesman Trent Duffy declined Sunday to answer questions about the administration's internal discussions.

Many Democrats and some Republicans in Congress have questioned whether Bush's actions went beyond the constitutional powers and congressional resolution he has cited. In 1978 Congress established a secret court to handle sensitive requests for surveillance and to issue warrants — a system the NSA program bypassed.

Sen. Arlen Specter (news, bio, voting record), the Pennsylvania Republican who chairs the Judiciary Committee, has called for hearings into the program. Sen. Mitch McConnell (news, bio, voting record), R-Ky., said Sunday that he would prefer that any hearings be held by the Intelligence Committee, which likely would be in secret.

"We're already talking about this entirely too much out in public as a result of these leaks ... and it's endangering our efforts to make Americans more secure," McConnell said.

Appearing with McConnell on "Fox News Sunday," Sen. Charles Schumer (news, bio, voting record), D-N.Y., said the Justice Department investigation should explore the motivation of the person who leaked the information.

"Was this somebody who had an ill purpose, trying to hurt the United States?" Schumer asked. "Or might it have been someone in the department who felt that this was wrong, legally wrong, that the law was being violated?"

Schumer released a letter he sent to Specter suggesting that current and former administration officials, including Comey and Ashcroft, be called to testify and that the administration waive executive privilege.

Sen. Richard Durbin (news, bio, voting record), D-Ill., appearing with Lugar on "Late Edition" on CNN, agreed with Lugar that Congress will focus in the new year on presidential powers in wartime.

"The White House wants to expand that power in so many areas," Durbin said. "Clearly, Congress is holding back."