Americans remain strong, it has been said, because "they have no memory." But last week, a memory - worse, a nightmare - turned up in Washington in the form of a half-paralyzed former prime minister.

He held a news conference outside a locked embassy building, a sad symbol of the serene little country of Cambodia, which he once ruled. Lon Nol, now a frail 66, sat in a wicker chair borrowed from a nearby furniture store, with its price tag still on it. Haltingly, he tried to explain to reporters the tragedy that has befallen his countrymen under communist rule.

Now banished to a small fruit farm in Hawaii, Lon Nol is almost a forgotten footnote in the catacylsm of Cambodia. His eyes reflect the sorrow and the tragedy of what has occurred in the aftermath of the Vietnam War.

The Cambodians are a gentle if emotional people. They wanted only to live in peace in their lush kingdom, with its rich alluvial soil, washed by the pelting rains. But with the collapse of U.S. power in Southeast Asia, Lon Nol gave way to a fanatic regime that has brutalized the populace. Hundreds of thousands have been murdered by their new rulers, and other thousands have fled in terror.

Enthroned in his lawn chair, Lon Hol was flanked by his entire entourage, which has been reduced to five aides. Our associate Tom Rosenstiel attended the news conference. Lon Nol had difficulty reading a prepared statement. His voice wavered amid long pauses. At one point, he just gasped helplessly into the microphone.

Subsequently, Rosenstiel repaired to Lon Nol's quarters for a private interview. The former chief of state was not staying at an expensive suite in one of Washington's hotels but in a modest room at the Silver Spring Holiday Inn. Throughout the interview, they were interrupted several times by hotel management trying to clear the room for incoming guests.

Lon Nol had come to power back in 1970 as head of the once-placied Cambodia and had accepted multimillion-dollar aid from the United States in exchange for the surreptitious use of the country for American-based attacks on the Viet Cong.

Lon Nol was a protege of the Nixon administration. One of his first U.S. visitors in Cambodia was Gen. Alexander Haig. At the meeting, according to U.S. aides, the Cambodian ruler unexpectedly broke down and sobbed. He told Haig in an agonized voice thathe lacked the understanding to confrot his country's problems or to muster the support of the Cambodian people.

American intelligence cables in 1971 reflect the deteriorating situation. They quoted high-placed Cambodian sources as saying "the recent military reverses appeared to have caused Lon Nol to take leave of his senses." Other secret cables to Washington reported that the prime minister's top officials had urged him to "relinquish active direction" of the government.

State Department officials have informed us that, although they doubted Lon Nol's capacities at the perilous time, they feared even more the disruption that his removal from office might cause. Other officials acknowledged that Cambodia was needed only to help win the war in Vietnam. In blunt terms the United States was willing to use Cambodia as an Asian cat's paw.

The aging, exiled former ruler recalled that, while some adviser told him the United States would sacrifice his country, he steadfastly believed that Nixon and the American people cared about his people and their fate. State Department sources told us he made a written request for help to Nixon in 1971. He asked Nixon how to run a modern country, eliminate corruption and fight modern wars against guerrilla forces.

A letter was drafted at the State Department trying to proffer advice. But when it went to the Nixon White House for clearance, it came back with a terse comment that "the president does not address matters of substance" on such questions. At about the same time, our diplomats in Cambodia, in their reports to Washington, criticized Lon Nol's "haphazard, our-of-channel and ill-coordinated conduct of military operations."

How deeply involved the Central Intelligence Agency was in Lon Nol's rise to power also remains an enigma. CIA trained troops, known as Khmer Serai, are known to have infiltrated the country just prior to the coup that deposed Prince Sihanouk. But Cambodian sources told us the CIA soldiers failed to get near the capital on Lon Nol's behalf.

In the private interview, however, the deposed leader admitted that the leader admitted that the leader of the CIA-trained Cambodian cadres, Son Ngac Than, was quickly brought in as an adviser once Lon Nol gained power.

He acknowledged that he had failed todeal with corruption in his government. His armies were filled with imaginary "phantom" soliders whose pay went into the pockets of generals. Inflation skyrocketed so drastically that the Cambodians almost had to resort to illegal blackmarket operations.

Lon Nol's brother and close adviser, Lon Non, was given the hook because of his corruptions. Enroute to exile Lon Nol's wife was found by French authorities toting a toy poodle stuffed with $170,000.

The former Cambodian strongman stated with quiet dignity: "I have come to Washington now because the killing has gone on too long."