WASHINGTON – Attorney General Alberto Gonzales offered additional defenses of President Bush’s wiretapping program yesterday, as the administration tried to redefine the warrantless surveillance in a way that undermines critics.

Speaking to students at Georgetown University law school, Mr. Gonzales said a 15-day grace period allowing warrantless eavesdropping under the Foreign Intelligence Surveillance Act demonstrates that Congress knew such surveillance “would be essential in wartime.”

Mr. Gonzales was supplying legal arguments to the president’s comments Monday that the effort should be called a “terrorist surveillance program.”

Confronting Mr. Gonzales during his nearly half-hour speech were more than a dozen young people in the audience who turned their backs to him and held up a banner for television cameras. The banner, loosely based on a Benjamin Franklin quote, read: “Those who would sacrifice liberty for security deserve neither.”

Before his appearance at Georgetown, Mr. Gonzales said in a television interview that some congressional leaders told the administration in 2004 that it would not be possible to write legislation regarding the warrantless surveillance effort without compromising its effectiveness.

“We did go to certain members of the congressional leadership a year and a half ago,” Mr. Gonzales said on CBS’s “The Early Show.”

During his remarks in a packed law school lecture room at Georgetown, the attorney general also said the legal standard the administration uses in deciding whether to carry out surveillance on people with suspected Al Qaeda ties is equivalent to the standard required for complying with the Fourth Amendment, which bans unreasonable searches and seizures.

The reasonable basis standard, said Mr. Gonzales, “is essentially the same as the traditional Fourth Amendment probable cause standard.”

Stephen Saltzburg, a law professor at George Washington University, said that Mr. Gonzales’ comments do not explain why the administration doesn’t go to the Foreign Intelligence Surveillance Court to obtain warrants.

“If they are using a probable cause standard, they would have no problem going to the FISA court,” said Mr. Saltzburg. “The executive might think there’s a reasonable basis. Courts might not agree.”

Georgetown University law professor David Cole said the reasonable basis standard is not equivalent to probable cause. Moreover, said Mr. Cole, Gonzales’ comments seem to conflict with those on Monday by Air Force General Michael Hayden, principal deputy director of national intelligence.

General Hayden said that when weighing whether to proceed with surveillance under the president’s program, “the trigger is quicker and a bit softer than it is” with FISA.

Justice Department spokeswoman Tasia Scolinos said there is no conflict between the statements of Mr. Gonzales and General Hayden and that “it is really just a matter of speed; as the AG said, the standards are essentially the same.”

In his address, Mr. Gonzales said, “I keep hearing, ‘Why not FISA?’ Why didn’t the president get orders from the FISA court?

“It is imperative for national security that we can detect reliably, immediately, and without delay whenever communications associated with Al Qaeda enter or leave the United States.”

Mr. Gonzales told his audience: “You may have heard about the provision of FISA that allows the president to conduct warrantless surveillance for 15 days following a declaration of war. That provision shows that Congress knew that warrantless surveillance would be essential in wartime.”