The U.S. invasion of Cambodia and military support for Lon Nol's government were decisions forced upon then-president Nixon by North Vietnam's actions, former secretary of state Henry A. Kissinger writes in an excerpt of his memoirs devoted to Indochina being published in Time magazine Monday.

In this first volume, spanning his years as Nixon's national security affairs adviser, Kissinger labels his Indochina critics "revisionists" who misconceive the facts of the Cambodian and Vietnamese wars.

Kissinger reveals for the first time that on April 4, 1970, before the invasion of Cambodia was planned, he urged North Vietnam's negotiator in Paris, Le Duc Tho, to discuss immediate measures to ensure Cambodia's neutrality -- either bilaterally or in an international framework.

Tho dismissed the suggestion. Kissinger writes that the North Vietnamese leader stressed, "It was his people's destiny not merely to take over South Vietnam but to dominate the whole of Indochina."

At the time of Kissinger's proposal, a Lon Nol coup had overthrown Prince Sihanouk, but survival of the Lon Nol government appeared uncertain.

If Lon Nol collapsed, Kissinger writes, the United States "would confront all of Cambodia as a communist base stretching 600 miles along the border of South Vietnam. Vietnamization and American withdrawal would then come unstuck.

"So we were being driven toward support of Lon Nol hesitantly, reluctantly, in response to circumstances in Cambodia that we could neither forecast nor control."

Nixon and top advisers met to consider invading Cambodia on April 22, 1970, Kissinger writes. The president said he favored using only South Vietnamese forces to enter Cambodia, Kissinger writes. Then vice president Agnew spoke up. "If it was worth cleaning them out he did not understand all the pussyfooting about the American role or what we accomplished by attacking only one" of their sanctuaries, Kissinger writes.

"Agnew was right," Kissinger declares in recording that Agnew's advice carried the day. But that was an exceptional case. In general, Kissinger says, "The bane of our military actions in Vietnam throughout was their hesitancy and inconclusiveness."

After the final meeting on the Cambodian invasion, Nixon invited Kissinger, attorney general John Mitchell and Charles G. (Bebe) Rebozo for a Potomac cruise on the presidential yacht Sequoia.

"The tensions of the grim military planning were transformed into exultation by the liquid refreshments," Kissinger writes. It was decided that everyone should stand at attention while the yacht passed Mount Vernon -- "a feat not managed by everybody with equal success," Kissinger recalls.

The party returned to the White House for a screening of Nixon's favorite movie, "Patton."

Kissinger's first volume of memoirs, called "White House Years," will be published Oct. 23 by Little, Brown.

The 13-page Indochina excerpt defends Nixon administration foreign policy actions at every crucial point -- the secret bombing of Cambodia, the "Christmas bobming" of North Vietnam, the mining of North Vietnam's harbors, and the conduct of the peace negotiations for which Kissinger was awarded a Nobel Peace Prize.

"I cannot yet write about Vietnam except with pain and sadness," his excerpt begins.

Kissinger expresses scorn for some of those who challenged the rightness of his decisions at the time.

While he says he considered the "idealism" of students and professors protesting the war as "indispensable for our future," and says this diverged from Nixon's view of protesters as an enemy to be conquered, Kissinger scathes the Harvard professors who visited him after the Cambodian invasion. He describes himself as having come to favor the invasion after a long period of hesitation because there was no alternative.

The meeting with the professors completed his transition from the academic world to the world of affairs, he writes. His former colleagues showed a lack of compassion and "overweening righteousness," he writes. They failed to offer him an alternative to the invasion and convinced him they would be of no help in his efforts to end the war.

The decision to mine North Vietnam's harbors was "one of the finest hours" of Nixon's presidency, Kissinger writes. He says Nixon played a game with him that forced him to make a strong and apparently unnecessary verbal defense of the mining decision. He realized a possible reason for the game only when he learned of the White House tape-recording system, Kissinger writes.

Some Nixon aides were unhappy, Kissinger writes, that some journalists were blaming Nixon for unpopular foreign policy moves while crediting Kissinger for popular ones. Nixon's aides resented Kissinger's good standing in the Georgetown "social set" that the president hated.

Kissinger says that this impression was fueled by the most "disastrous conversation I ever had" with a member of the press. In an interview with Italian journalist Oriana Fallaci, Kissinger describes himself as a lone cowboy, an "amazing, romantic character," and in his memoirs he declares the Fallaci interview contains "the most self-serving utterances of my entire public career."

He also confesses to "a not very heroic desire" to defelct some of the criticism of the Christmas bombing from himself. This desire led him not to deter speculation that he had taken a "softer" position.

"Nixon was justifiably infuriated by assertions that I had opposed the bombing," Kissinger writes.

As a result of the rift developing between himself and the president, Kissinger recounts that he decided to retire from office.

Kissinger says that he planned to carry through the Vietnam peace negotiations, but if they collapsed he would resign and take full responsibility, and if they succeeded he would resign in late 1973.

The negotiations, of course, did not collapse. Kissinger did not resign.

Instead, Nixon made him secretary of state, and Kissinger is preparing a second volume of memoirs on those years.

Because of Watergate, he could not carry out his plan to leave office, Kissinger writes without explanation. Presumably, he felt he could not leave a president who had become so embattled.