WASHINGTON  President Bush on Saturday further cemented his legacy of fighting for strong executive powers, using his veto to shut down a congressional effort to limit the Central Intelligence Agency’s latitude to subject terrorism suspects to harsh interrogation techniques that are prohibited by the military and law enforcement agencies.

Mr. Bush vetoed a bill that would have explicitly prohibited the agency from using such interrogation methods, which include waterboarding, a technique in which restrained prisoners are threatened with drowning and that has been the subject of intense criticism at home and abroad.

Mr. Bush’s veto deepens his battle with increasingly assertive Democrats in Congress over issues at the heart of his legacy. As his presidency winds down, he has made it clear he does not intend to bend in this or other confrontations with Congress on issues from the war in Iraq to contempt charges against his chief of staff, Joshua B. Bolten, and former counsel, Harriet E. Miers.

Mr. Bush announced the veto in the usual format of his weekly radio address, which is distributed to stations across the country each Saturday. In his remarks, he unflinchingly defended an interrogation program that has prompted critics to accuse him not only of authorizing torture previously but also of refusing to ban it in the future.