Not even the Pentagon's most inventive war-game players could think it up: war has been raging for three weeks in a vital area between a close American ally and a Soviet client; Moscow and Washington have brokered a cease-fire, but it is breaking down. The Soviets deliver a rough ultimatum: either both sides intervene with peacekeeping forces, or they will move in on their own.

The National Security Council is rushed to the White House "situation room" to plot a quick counter-strategy. But the NSC's statutory chairman, the president, is not in the chair. He is incapacitated upstairs in the living quarters; a "paralyzing" domestic crisis has left him "too distraught to participate." The 25th Amendment makes provision for transfer of authority to the vice president when the president is unable to function -- but there is no vice president.

Besides, only the secretary of state and the White House chief of staff are aware of the president's condition. A majority of the "principal officers" of the executive branch will have to make the decision.

Not possible? But of course it did happen -- on the night of Oct. 24, 1973. By now you may have recognized the occasion, the so-called Yom Kippur War between Israel and Egypt (plus Syria), and the leading figures: Richard Nixon as president, Henry Kissinger as secretary of state; Alexander Haig as chief of staff. The "missing" vice president was Gerald Ford, designated by Nixon but not yet confirmed by Congress to replace Spiro T. Agnew.

What you may not have recognized, in this version of the famous night when the United States went on nuclear "alert," is the characterization of the role of the president (not, that is, if you remember the official line at the time). Yet that is pretty much the way it comes across in a revealing account in the second volume of Henry Kissinger's memoirs, "Years of Upheaval."

At a time when government and the media are once again in a slanging match over who's telling the truth -- about El Salvador or the economy -- the Kissinger version of the October War is a timely reminder that almost never is either side blameless in these matters. The argument is essentially unwinnable. And anything as absolute as truth is unattainable, even with the passage of time.

Kissinger's 162-page account adds enormously, and meticulously, to the record of one of the most controversial and crisis-laden three weeks in American political and diplomatic history. In the period between Oct. 6 (when the war broke out) and Oct. 28 (when the Egyptians and Israelis met to negotiate a disengagement of forces), Agnew resigned in disgrace and Nixon's Watergate fate was sealed by the Saturday Night Massacre and an appeals court ruling that he would have to surrender the Oval Office tapes.

But such is Kissinger's artful ambivalence that it is impossible to determine from one episode to another whether he thinks Nixon, under terrible pressure, was unfit for duty or was in command.

One day, Oct. 24, captures the perils as well as emotions, frustrations, suspicions and generally rancid atmosphere. The cease-fire had collapsed. The Egyptians were calling for intervention by American and Soviet troops. Kissinger was meeting with Dobrynin when Nixon, "as agitated and emotional as I had ever heard him," phoned. His enemies, Nixon told Kissinger, "are doing it because of their desire to kill the president. And they may succeed. I may physically die."

Nixon went on: "What they care about is destruction....The real tragedy is if I move out, everything we have done will crumble.... They just don't realize they are throwing everything out the window. I don't know what in the name of God..."

This was enough for Kissinger to decide to take Haig's advice -- when three hours later the Soviets threatened to intervene unilaterally -- and not "wake up the president," who had apparently "retired for the night." There is no evidence that Nixon talked with anybody (other than Haig) while the decision was being made in the early hours of the following morning to put American forces on alert and put the United States at risk of nuclear war.

That the crisis was real, Kissinger leaves little doubt -- though suspicions ran high at the time. That Nixon sought repeatedly to exploit it to demonstrate his "indispensability" (as impeachment loomed), Kissinger amply documents. That Nixon was repeatedly "out of touch," "obsessed," "preoccupied," "on the verge" (as Haig cryptically put it), "in the paralysis of as approaching nightmare" -- all this Kissinger makes plain. On that score, his account gives the lie to White House accounts at the time.

But as to a clear judgment, Kissinger speaks ambiguously of a Nixon overwhelmed by his "persecutors," of Watergate as "extralegal" activities, of a "nation consuming its authority." The insights and information are spellbinding. But in a matter of historic interest, we are left not all that much closer to the "truth" than we were at the time