President Richard M. Nixon and his top aides, H.R. Haldeman and Henry A. Kissinger, talked in 1971 about getting secret documents that could be used to "blackmail" Lyndon B. Johnson over the war in Vietnam.

The discussion appears to have sparked Nixon's determination to break into the Brookings Institution and raid its files. What Nixon wanted was the inside story of the 1968 bombing halt over North Vietnam that President Johnson ordered a few days before the election, and that Nixon believed almost cost him the White House. Kissinger said he "wouldn't be surprised if Brookings had the files on the bombing halt."

The Oval Office conversation took place on June 17, 1971, during a dramatic conflict between the government and the press over publication of a secret Defense Department history of the war known as the "Pentagon Papers."

Nixon, White House Chief of Staff Haldeman and Kissinger, then national security adviser, have obviously been talking about the papers when the taped segment, recently made available at the National Archives, begins.

"You can blackmail Johnson on this stuff," Haldeman said.

"What?" Nixon responded quickly. He always suspected that Johnson had stopped the bombing as a political ploy, to help the Democratic candidate, Vice President Hubert H. Humphrey, overcome Nixon's lead. Now Nixon wanted Johnson to do him a favor by publicly denouncing the publication of the Pentagon Papers.

"You can blackmail Johnson on this stuff and it might be worth doing," Haldeman said.

"How?" Nixon asked.

"The bombing-halt stuff is all in the same file," Haldeman said. "It's in the same hands."

"Oh, how does that shape up?" the president said. "It isn't in these papers," Haldeman said, alluding to the fact that the secret history ended in early 1968, months before the bombing halt that Nixon, in his memoirs, said "unquestionably resulted in a last-minute surge of support for Humphrey." However, Haldeman added, "the whole bombing halt file -- "

"Do we have it?" Nixon interrupted. "I asked for it. You said you didn't have it."

Haldeman said "we can't find" it.

"We have nothing here, Mr. President," Kissinger interjected.

"Goddammit, I asked for it," Nixon said. "I said I needed it. . . ."

Kissinger said he and Haldeman had been trying to compose their own study.

"Bob and I have been trying to put the damn thing together for three years," Kissinger said.

Haldeman added: "We have a basic history. We constructed our own. But there is a file on it."

"Where?" Nixon demanded.

"Huston swears to God there's a file on it at Brookings," Haldeman said, referring to White House aide Tom Charles Huston.

"I wouldn't be surprised," Kissinger said.

Nixon, as he later wrote, was "furious and frustrated." He had asked Haldeman soon after taking office to get him a copy of the Pentagon file on events leading up to LBJ's bombing halt. Now he was being told that "top-secret government reports were out of reach in the hands of a private think tank largely staffed with antiwar Democrats. It seemed absurd."

On the tape, Nixon said: "Now if you remember Huston's plan -- "

Huston in 1970 recommended lifting restraints on intelligence gathering and resuming surreptitious entries, covert mail covers and the like, even though they were illegal. Nixon had approved the plan, but it was withdrawn after opposition from FBI Director J. Edgar Hoover and Attorney General John N. Mitchell.

"Yeah, why?" Haldeman asked.

Kissinger interjected: "But couldn't we go over? Now Brookings has no right to classified -- "

The president didn't let Kissinger finish. "You know why," Nixon told Haldeman. "I mean I want it {the Huston plan} implemented. . . . Goddammit, get in and get those files. Blow the safe and get them."

In his memoirs, Nixon acknowledged in softer language that he wanted the bombing halt file from Brookings, "even if it meant having to get it surreptitiously." But he didn't use the word "blackmail," and he didn't mention LBJ directly. Nixon wrote that he simply "wanted to know what actually happened" and that he "also wanted the information as potential leverage against those in Johnson's administration who were now trying to undercut my war policy."

Nixon ordered a break-in at the Brookings at least twice more, on June 30 and July 1, 1971, at one point pounding on the desk in exasperation that his aides had not pulled it off. They never did, according to officials at Brookings. In any case, "there were no classified documents at all at Brookings. . . . It was all just their own paranoia," said Morton Halperin, a former Defense Department official who was then working at the think tank. Kissinger spokesman Jerry Bremer said he did not see the tape "as an endorsement {by Kissinger} of a surreptitious entry. It's ambiguous."