Chilling, revealing and acrimonious by turns, last week's hearings before the Senate Select Committee on POW-MIA Affairs was another bitter chapter in the history of the Vietnam War-and an attempt, as it were, to prove the existence of ghosts. There were various estimates: 67 ghosts, 133 ghosts, possibly as many as 478 ghosts. The ghosts had names, ranks and serial numbers and relatives who, nearly 20 years after the U.S. withdrawal from Vietnam, followed the Senate hearings with anguished fascination. This was the moment when those who kept the secrets came forward to say in public what they had never said before. Yes, the U.S. government had reason to believe that at least some Americans were left behind when Richard Nixon announced in 1973 that all surviving U.S. POWs had returned from Vietnam. But no one could answer the all-important question: are any of the missing still alive?

It is, sad to say, less than likely that this question will ever be answered. But nothing about the endless quest for U.S. POWs and MLAs in Southeast Asia is simple, and no one can rule out the possibility that someone has survived. What was certain, last week, was that many top U.S. officials never accepted Nixon's assurances to the nation in 1973: there was too much evidence to the contrary in the secret files. And it was also clear, in the rancorous exchanges that marked the testimony of former secretary of state Henry Kissinger (page 50), that Vietnam is still brutally divisive. "It is no great achievement to go picking through bureaucratic documents and use one sentence to prove what the [administration's] motive was," an angry Kissinger told Democratic Sen, John Kerry, a Vietnam veteran and prominent opponent of the war. "Sir, this is not a 'bureaucratic document'," Kerry retorted. "This is an American serviceman who was held as a prisoner in Vietnam."

Kerry's committee aims to settle the question of just how many U.S. servicemen were left behind in 1973-and then, if possible, to press for a final accounting from the tight-lipped apparatchiks in Hanoi. But the target last week seemed to be Kissinger, the architect of the Paris peace accords and the man who, with Le Duc Tho of North Vietnam, shared the 1973 Nobel Peace Prize for helping to end the conflict in Vietnam. Kissinger angrily defended the Nixon administration's decision to negotiate the U.S. withdrawal from Vietnam despite allegations that U.S. officials knew the list of 591 returning POWs was almost certainly incomplete. That allegation was an "unforgivable libel," Kissinger said vehemently. "No confirmed report of living American prisoners ever crossed my desk," he said, "although I am not saying they did not exist."

The caveat was crucial, given the testimony of former defense secretaries Melvin Laird and James Schlesinger. Schlesinger said he had a "high-probability assessment that people were left behind in Laos, and a medium probability with regard to Vietnam." Laird said he had a "gut feeling" that some POWs were never released and that Pentagon officials regarded letters from the POWs themselves as the best evidence that Hanoi's accounting was not complete. These letters, which were received by POW families in the United States between 1960 and 1972, suggested to U.S. analysts that as many as 474 or 478 POWs-Laird couldn't remember which-had never been included in Hanoi's lists, thus raising the question whether some or all had been left behind. (At this point, according to The New York Times, between 100 and 200 POW/MIA reports are regarded by U.S. officials as credible but unresolved.) Schlesinger said the chances were "very slim" that any of the POWs were still alive-and retired Gen. Vernon Walters, former deputy director of the CIA, said he thought their captors had simply killed them.

The thrust of this testimony was to suggest that-wittingly or not-Nixon and Kissinger had abandoned hundreds of Americans in Southeast Asia. Kissinger argued that no one could have done more than he and Nixon did, and that congressional restrictions on the use of military force in Southeast Asia prevented them from putting pressure on Hanoi to live up to its agreement to account for all U.S. POWs. "If servicemen were kept by our enemies, there is one villain and one villain only-the coldhearted rulers in Hanoi," he said. Winston Lord, a former Kissinger aide, said he supported the decision to withdraw because "American society would have blown apart" if Nixon had bombed North Vietnam over the "very disturbing evidence ... of discrepancies" in the POW lists. "The president decided not to scuttle [the Paris peace] agreement over the MIA issue," Lord said. "It was a very tough decision."

There were plenty of precedents from previous administrations. Recently unearthed evidence indicates that hundreds and perhaps thousands of U.S. POWs may have been abandoned by their government during the cold war, in the aftermath of the Korean conflict and even as early as World War II. Stunned by Boris Yeltsin's admission last summer that U.S. prisoners from World War II and Korea had been detained in the Soviet Union, the Bush administration is pushing a joint U.S.-Russian attempt to trace fragmentary reports of American prisoners once held in the Gulag. Last week the Russians handed over reports on 54 Korean War POWs who had been interrogated by Soviet and Chinese agents in China, along with Soviet records on U.S. pilots who were shot down on secret missions in the cold-war years.

The documents included a stunning exchange of secret telegrams between Joseph Stalin, Mao Zedong, Zhou Enlai and North Korea's Kim II Sung, in which the Chinese proposed that 20 percent of all U.S. POWs from the Korean War be detained for use as diplomatic leverage on Washington. The messages broadly support one of the most dramatic POW stories of all-the allegation that between 800 and 1,200 U.S. prisoners were rounded up by Chinese or North Korean troops and shipped north through Manchuria to the Soviet Union. (The story appears in a newly published book by three American journalists, "Soldiers of Misfortune: Washington's Secret Betrayal of American POWs in the Soviet Union.")

According to retired army Col. Philip Corso, who wrote a top-secret report on the incident for President Dwight Eisenhower in 1953, the Soviets' probable motive was espionage: the POWs would be interrogated about the details of their lives, and these life histories would then be supplied to Soviet spies for use as cover stories. Corso says he told Eisenhower the POWs should be given up for dead. "Is this your recommendation, Colonel?" Eisenhower said. "What can I recommend?" Corso replied. "Based on what I know of Soviet policy, these boys will never come back alive." Eisenhower Corso says, shook his head and agreed. "The fear of general war [with the Soviet Union and China] tied our hands," Corso says. "We never said anything to the families. We didn't know what to say."

Malcolm Toon, a former U.S. ambassador to the Soviet Union who now heads the U.S. investigative team in Moscow, said last week, "There is no question in our minds" that large numbers of U.S. POWS from Korea were shipped to the Soviet Union. Toon said Yeltsin's government was eager to cooperate, but that the search for information about these POWs was being frustrated by resistance from elements of the former KGB and the GRU, Russian military intelligence. The Americans "were interrogated, imprisoned, maybe killed," Toon said. "We're trying to pin this down now." Meanwhile, he said, "the question about the same thing happening during the Vietnam War is much more murky--there's very little evidence of that." So far, he said, "I have seen nothing that would indicate there is a live American POW here." But the search for POWS will continue, very possibly for years-while Americans, and particularly the families of the missing, can only wonder whether the whole truth has yet been told.