LT. COL. Oliver North told an acquaintance several years ago that he was worried that if the United States ever abandoned the contras, the Nicaraguan rebels might someday turn their guns on us.

North was probably exaggerating in that remark, as in so many other things. But he had a point. Whatever we think of the contras, we all have a practical reason for wanting a settlement in Central America that will allow them to go back home, live in peace -- and put down their weapons for good.

Our stake in what happens to the contras is partly a matter of self-interest. If we can't find a settlement that will allow the Nicaraguan rebels to go home, we may someday have thousands of disgruntled ex-contras haunting the streets of Miami and New Orleans, not to mention Tegucigalpa. If you want an example of just how disruptive they could be, take a look at the Bay of Pigs veterans, who are still getting into trouble more than 25 years after they were recruited and abandoned by the CIA.

We also have a moral obligation to the contras, even if we oppose further military aid for them. By an act of Congress, the United States armed the contras, trained them, encouraged them to risk their lives and sanctioned their killing of others. If we now decide to withdraw our assistance, we have a special obligation to find a peace settlement that will allow the contras and their supporters to live in Nicaragua without fearing for their lives.

Peace prospects seemed to improve slightly last week, with President Reagan's proposal for a cease-fire in Central America. The Reagan plan called for national reconciliation and dialogue in Nicaragua, including amnesty for former combatants and an opportunity for all groups to take part in politics. On Friday, the leaders of five Central American countries endorsed a similar peace plan, in which a general political amnesty would be supervised by a National Reconciliation Commission made up of representatives from the government, opposition parties, and the Catholic Church.

The contras say that about 500,000 Nicaraguans, or about 20 percent of the population, are now living in exile -- roughly half of them in the United States. The contras also claim to have 15,000 troops in the field. These exiles and fighters won't return home without "a climate of political goodwill that will allow a democratic political processs," according to Bosco Matamoros, the contras' military spokesman in Washington. Establishing such a democratic Nicaragua, alas, is what the war has been all about.

Reconciliation obviously won't be easy. Both sides have blood on their hands. The contras say they have suffered more than 5,000 dead since 1980, and that more than 500 of their fighters have lost arms or legs. The Sandinistas have similar tales and totals. With so many scores to settle, the bloodletting could go on for a generation. This makes amnesty all the more difficult -- and necessary.

The amnesty problem illustrates why it's much simpler to start a paramilitary operation than it is to stop one. Once the CIA's recruits are in the field -- fighting and dying at the behest of the United States -- we incur a profound moral responsibility. If we decide later that it's best to withdraw, we need to take care of our people, rather than leaving them at the mercy of their enemies.

We should have learned this lesson long ago -- at the Bay of Pigs, in Vietnam, in Lebanon, and in the half-dozen other Third World wars where we left our allies hanging. We Americans have a particularly nasty way of recruiting people to do our dirty work and then abandoning them when we have second thoughts. In most cases, we never should have embarked on the military adventures in the first place. But that doesn't lessen our obligation to those who took up arms at our urging.

The Bay of Pigs debacle is the most worrisome analogy for what may happen to the contras. David Atlee Phillips, a 25-year CIA veteran, wrote in these pages last year about the slaughter of the CIA-backed Cuban invasion force in 1961. He recalled the horrifying final moments: "The Cuban exile military commander of Brigade 2506 was about to abandon the fight. In what was to be his final radio report, his voice was clear. There was no static to muffle the obscenities he used to describe the American government. He cursed us as individuals."

Some of the Cuban exiles who survived the Bay of Pigs are still cursing, 25 years later. They have haunted our national life, surfacing regularly in investigations of our national traumas -- from the Kennedy assassination to Watergate to the Iran-contra affair.

The lesson is that veterans of paramilitary operations don't just fade away. They find employment in unusual and often dangerous ways. Think of the Cuban exiles -- Sturgis, Martinez, Barker -- who worked with Howard Hunt in the Watergate bugging operation. Think of "Max Gomez" and "Ramon Medina," two Cuban exiles who eventually turned up as part of Oliver North's secret army in Central America.

Vietnam provides another example of the trauma that follows a failed military campaign -- and the moral anguish felt by soldiers and CIA officers who leave their allies behind to die.

Frank Snepp, a CIA analyst in Saigon during the final days of the war, recorded that sense of shame in his book "Decent Interval." He writes that the CIA managed to evacuate only about 537 of the Saigon station's 1,900 "indigenous employes" when the Americans pulled out in April 1975. Also left behind were 400 members of the CIA-trained Special Police Branch; 400 members of the Central Intelligence Organization of South Vietnam; hundreds of North Vietnamese and Vietcong defectors; and as many as 30,000 counterterrorism agents who had been trained as operatives in the CIA's Phoenix program. In addition, writes Snepp, "we committed the unpardonable mistake of failing to ensure the destruction of the personnel files and intelligence dossiers we had helped the government assemble."

Snepp concludes: "It is not too much to say that in terms of squandered lives, blown secrets, and the betrayal of agents, friends and collaborators, our handling of the evacuation was an institutional disgrace."

The Reagan administration now seems willing to consider a negotiated settlement of the covert war in Central America, just as we negotiated an end to the Vietnam War in the early 1970s. That is certainly the sensible course. But advocates of negotiation should try to avoid pulling the plug on the contras in a way that compounds the damage that the war has already done.

Even as we take steps to end the war, the United States should keep faith with the contras -- who took our money and our word -- by making sure that they can go home again.

David Ignatius, an associate editor of The Washington Post, edits the Outlook section.