Lawmakers are arguing over the legality of intercepting international communications among suspected terrorists and questioned President Bush's authority to direct the National Security Agency to monitor phone calls without a court-approved warrant.
Bush acknowledged last weekend that he authorized NSA to intercept international calls and e-mails but only those linked to Al Qaeda, even if one end of the conversation is taking place in the United States and includes an American citizen.
Click in the video box to the right to watch a report by FOX News' Jim Angle.
"How do we effectively detect enemies hiding in our midst and prevent them from striking us again? We know that a two-minute phone conversation between somebody linked to Al Qaeda here and an operative overseas could lead directly to the loss of thousands of lives," Bush said during a Monday press conference.
Just before the terror attacks on the Pentagon and World Trade Center on Sept. 11, 2001, two of the hijackers called Afghanistan, perhaps for final instructions — exactly the kind of communication Bush said he is now determined to intercept.
Some argue that the president must get a warrant from what is known as the Foreign Intelligence Surveillance Act court, which operates in secret. The president suggested that going through the court to get a warrant would have taken too long.
"The people responsible for helping us protect and defend came forth with the current program because it enables us to move faster and quicker," Bush said.
Congressional critics also argue that the president has taken the law into his own hands and he doesn't have the authority to order electronic intercepts of anyone in the United States without getting a search warrant.
"Where does he find in the Constitution the authority to tap the wires and the phones of American citizens without any court oversight?" asked Sen. Carl Levin, D-Mich., ranking member of the Senate Armed Services Committee.
"The American public is given vague and empty assurances by the president that amount to little more than, 'Trust me. Trust me,'" said Sen. Robert Byrd, D-W. Va.
Sen. Barbara A. Mikulski, D-Md., called for the Senate Intelligence Committee, of which she is a member, to hold expedited hearings into the matter.
"The president seems to have admitted that he secretly eliminated this entire legal process. That raises very serious questions about U.S. intelligence operations and about the president's commitment to obeying the law," Mikulski said.
Late Monday, Sen. Jay Rockefeller, D-W.Va., the ranking member on the Senate Intelligence Committee, said he too wants expedited hearings, including one into the leak to The New York Times, which first revealed the program. He added that he thought Bush, who called the leak "shameful," was "too weak" on that matter during his press conference.
In addition, Rockefeller said he was briefed on the program when he first took his position two years ago as vice chairman of the panel. He was told at the time that the program was top secret and he was not allowed to discuss it with anyone, including his chief of staff, "not even my wife."
Rockefeller also released a letter he wrote to Vice President Cheney two years ago, expressing what he called "lingering concerns" about the program, which he said raised "profound oversight issues."
"I feel unable to fully evaluate, much less endorse, these activities," he wrote in the July 2003 letter. "As you know, I am neither a technician nor an attorney."
"The president just keeps saying 'we informed Congress,' and it's so annoying. It's phony. It's totally phony," Rockefeller said.
Former Senate Democratic leader Tom Daschle said he, too, was briefed by the White House between 2002 and 2004 but was not told key details about the scope of the program.
Daschle's successor, Sen. Harry Reid, D-Nev., said he received a single briefing earlier this year and that important details were withheld. "We need to investigate this program and the president's legal authority to carry it out," Reid said.
On Tuesday, Sen. Pat Roberts, R-Kan., chairman of the intelligence panel, said if Rockefeller had a problem with the program, he had several avenues to raise concerns, including taking up the issue with other members who had been briefed, using legislative tools at his disposal or confronting the vice president during any one of several briefings.
"A United States Senator has significant tools with which to wield power and influence over the executive branch. Feigning helplessness is not one of those tools," Roberts told reporters in a written statement. "If Senator Rockefeller truly had the concerns he claimed to have had in his two and a half year old letter, he could have pursued a number of options to have those concerns addressed."
Bush argues he was authorized after Sept. 11 to use whatever force was necessary to combat the terrorists who had taken sanctuary in Afghanistan. He points to that as well as his constitutional powers to protect the nation as the basis for authorizing the intercepts.
"As president and commander in chief, I have the constitutional responsibility and the constitutional authority to protect our country. Article II of the Constitution gives me that responsibility and the authority necessary to fulfill it. And after September the 11th, the United States Congress also granted me additional authority to use military force against Al Qaeda," he said.
Decisions on what conversations to monitor are made at the Fort Meade, Md., headquarters, approved by an NSA shift supervisor and carefully recorded, said Gen. Michael Hayden, the principal deputy director of intelligence.
"The reason I emphasize that this is done at the operational level is to remove any question in your mind that this is in any way politically influenced," said Hayden, who was NSA director when the program began.
One national security lawyer said Bush does have solid constitutional authority to act.
"The highest court that's looked at these questions has said that the president has the inherent constitutional authority to use electronic surveillance to collect foreign intelligence and Congress cannot take away that constitutional authority. That's a pretty good argument," said Bryan Cunningham, a former legal adviser to the National Security Council.
Pennsylvania Republican Sen. Arlen Specter, chairman of the Senate Judiciary Committee, said he had already planned to hold hearings on this issue, and that an investigation into this program "ought to include what the chair and vice chair of intelligence ought to do in instances" where they are asked to keep secret programs that they believe violate the Constitution or U.S. law.
He and ranking Democrat on the panel, Sen. Patrick Leahy of Vermont, both said they also plan to raise the issue during the Supreme Court confirmation hearing of Samuel Alito. They want to ask the judge whether he thinks the president has the authority he claims.
Officials emphasize that warrants were not sought for any intercepts entirely within the United States, and several intelligence experts told FOX News that beyond that several circumstances exists under which the president is not obligated to obtain a warrant.
The administration is reluctant to talk about details, however. Officials call this the "most classified program in the U.S. government."
FOX News' Trish Turner contributed to this report.