They include a Jan. 5, 1973, conversation between Nixon and his aide Charles W. Colson in which they discussed the possibility of granting clemency to E. Howard Hunt Jr., one of the Watergate conspirators, according to a log compiled by archives staff. Scholars say the same topic was addressed in several other tapes that were previously made public.

The documents also include nine pages of handwritten notes by a domestic policy aide about plans for what the White House would say about the dismissal of the Watergate special prosecutor, Mr. Cox.

The tapes also provide new material about the circumstances surrounding the Paris treaty to end the United States’ military involvement in Vietnam.

A call between Nixon and Mr. Colson just after midnight on Jan. 20 showed that Nixon anticipated, when the treaty was announced, that he would be vindicated for continuing to bomb North Vietnam. He especially relished the hit that he believed members of Congress who opposed the war  whose public statements he pronounced “treasonable”  would suffer.

Several conversations center on the pressure Nixon placed on South Vietnam’s president, Nguyen Van Thieu, to accept the cease-fire agreement. Ken Hughes, a Nixon scholar and research fellow at the Presidential Recordings Project at the University of Virginia, said he was struck by listening on one of the new tapes to Nixon’s telling his national security adviser, Henry A. Kissinger, that to get Thieu to sign the treaty, he would “cut off his head if necessary.”

Mr. Hughes said the conversation bolstered his view that Nixon, Thieu and Mr. Kissinger knew at the time that the cease-fire could not endure, and that it was not “peace with honor,” as Nixon described it, so much as a face-saving way for the United States to get out of the war. In 1975, North Vietnam would violate the cease-fire and conquer South Vietnam.

The tapes also include a phone call from February 1973 between Nixon and the evangelist Billy Graham, during which Mr. Graham complained that Jewish-American leaders were opposing efforts to promote evangelical Christianity, like Campus Crusade. The two men agreed that the Jewish leaders risked setting off anti-Semitic sentiment.