Gonzales, a key architect of the surveillance program, said that the operation was ''both necessary and lawful'' and that he believed any president would have taken the steps Bush did.

''I think it would be irresponsible to do otherwise,'' he said in a speech at Georgetown University Law Center.

Gonzales' address, along with seven television appearances Monday night and Tuesday morning, was part of an orchestrated effort by the Bush administration to recast the debate on the National Security Agency program as one of national security rather than civil liberties. Gen. Michael Hayden, the nation's second-ranking intelligence official, made an unusual public speech about the program on Monday.

The president is also scheduled to visit the security agency in Fort Meade, Md., today to reassure employees whose normally secret activities have come under scrutiny.

With polls showing the public evenly split about the eavesdropping program, Gonzales - like Bush and Vice President Dick Cheney before him - said in his speech that he welcomed a ''worthy debate'' over the limits of presidential power.

More than two dozen students in the audience responded by turning their backs on Gonzales and standing stone-faced before live television cameras for the duration of his half-hour speech.