Chile haunts him.

He has been in the Foreign Service since 1947, so wedded to it that when asked if he ever wanted to do anything else he says simply, "I don't know." His assignments have included Bulgaria, Guatemala (where, since his predecessor had been murdered, he traveled with armed guards), Washington and Switzerland. But it was his two-year stint as U.S. ambassador to Chile that made Nathaniel Davis the model for the ambassador in the 1982 film "Missing" and left a scar on his life.

Last Monday, lawyers for Davis and two other embassy officials who served with him in Chile filed a $150 million libel suit in U.S. District Court in Alexandria against Universal City Studios Inc., which made "Missing," about the disappearance and death of American Charles Horman in Chile, and against Thomas Hauser, who wrote the book upon which the film is based. Also named were Constantin Costa-Gavras, the director of "Missing"; MCA Inc., the parent corporation of Universal; Harcourt Brace Jovanovich Inc., publisher of the hardcover book by Hauser; and the Hearst Corp., whose Avon Books division published the paperback version.

In the suit, the lawyers single out passages of the book and movie, stating they are "false, unfair, inaccurate and defamatory." The plaintiffs "have been held up to public disgrace, scorn, and ridicule," according to the suit.

"I've lived with the Horman case personally and professionally," Davis says quietly in an airport restaurant outside Providence, R.I. The case, he says, was not the reason he was brought back to Washington to become director general of the Foreign Service a month and a half after the young American's disappearance. "But it affected my career after that."

When he was nominated for assistant secretary for African Affairs in January 1975, the Organization of African Unity issued an unprecedented formal statement questioning his appointment because of the cloud cast over him by the suspicion of U.S. involvement in the coup in Chile. He was appointed to the post, but seven months later he resigned over the decision to increase covert U.S. intervention in the Angolan civil war. Davis went to Switzerland after that. He has been teaching at the Naval War College in Newport, R.I., since 1977.

The movie "Missing" and the book of the same name portray the U.S. ambassador to Chile -- who is called simply "the ambassador" -- as a defender of big business, with a veneer of ambassadorial politeness masking a deep coldness.

Sitting in a quiet restaurant, the 57-year-old former ambassador is polite and friendly but guarded in his answers. White-haired and portly, he clasps his hands and places them squarely on the table when talking or leans back in his seat, hands in the pockets of his dark, three-piece suit. Certain scenes in the movie make him indignant and resentful, he says, but if there is bitterness at his portrayal in the film and book, it doesn't show; if there is emotion it doesn't show; there's just a flicker of resignation.

"Well, it hasn't been a very happy experience," he says.

More than nine years have passed since Sept. 17, 1973, when Charles Horman, an adventurous, 30-year-old American free-lance journalist, was taken from his home in Santiago, Chile. In late October, his body was found in the municipal cemetery. In the weeks between, Horman's wife, Joyce, and his father, Edmund, took up a painful and arduous search for him in a country reeling from the military coup Sept. 11 that toppled the Marxist government of Salvador Allende.

It was a search, the Hormans have said, that U.S. embassy officials in Santiago not only didn't aid but actually hindered -- to the point where the Hormans suspected U.S. officials of complicity in Charles Horman's death, which allegedly occurred at the hands of the Children military. The Hormans suspected that Charles was murdered because he had, by chance, received sensitive information about American involvement in the coup through conversations with a naval engineer in Vina del Mar, Chile.

Nathaniel Davis picks his words carefully, and articulates them as deliberately as if he were speaking to one of his classes at the Naval War College.

Some of his own first-hand recollections of Chile and the Hormans are vague, but he's well-versed in the details of the book and the movie.

He has been the movie twice. The first time was when "Good Morning, America" arranged for him to see it a year ago in New York before making an appearance on the show to discuss the movie. The second time was recently, in preparation for questions after the filing of the lawsuit. He rented a video cassette recording of the movie in Newport for $4 and borrowed a machine on which to play it.

"Obviously, the movie has great dramatic impact, doesn't it?" he says with a little smile. " . . . I can certainly say what the impact of the movie brought home to me is that most people who see it end up believing it -- which is very bothersome.

"I was also said that this unhappiness and frustration of the family seemed to find its expression in turning on U.S. public officials who were trying to help them." He pauses and smiles slightly. "It was kind of said."

Despite this, he says he feels no resentment toward Edmund Horman, who has publicly expressed his dislike of the ambassador. "Whatever grief they've given me," Davis says, "they've suffered more."

That's why Davis excluded Edmund Horman from the suit.

"My own feeling is that Edmund Horman has lost his only child," says Davis. "He's a little different from people who are making a pile of money on saying things that are false about me and my colleagues and the U.S. public service. It's a little different.

"I understand what the family has gone through. Well, perhaps I don't understand. But I can understand what it's like to lose your son," adds Davis, who has four children. "I don't mean I've lost any of my children, but I think I can imagine what he feels like. That has to condition my feelings about him."

But not his feelings about the movie.

"The thrust of the movie essentially is that we were complicit in telling the Chileans to murder Charles Horman," says Davis. "Charles and Terry Simon [a visiting friend] went down to Vina and learned too much and... as a result of trying to suppress what they learned down there, we either agreed to or put the Chileans up to killing them. That's what the movie says or suggests. It's very bothersome to me, in the first place not only personally but for what this says about the U.S. Foreign Service, that an ambassador, who is a professional, would go abroad and be in the position of telling the authorities of another country to kill an innocent young American who's committed no crime. That's a very corrosive thing to suggest about public service when it's false."

"The movie does raise questions about government officials," says Sheldon Mittleman, the head of Universal's legal department. "We felt and still feel that it's not defamatory... I think Ambassador Davis sees a lot of innuendo that's not there. That's my personal opinion. I think the ambassador reads things in that aren't there. The courts will decide that down the line."

"I think that the complaint is an example of cheap-shot draftsmanship," says author Hauser, who is also a lawyer. "There's nothing in that suit that pertains to me that isn't virtually protected." Hauser points out that many of the statements from his book cited in the suit are quotes from other people.

"I have never said, nor has the book said, that any of the plaintiffs ordered the execution of Charles Horman," says Hauser. "Obviously, I've said some of the officials were not as forthcoming with information about the Horman case as they should have been."

Last year, Hauser says, he made a "generous offer" to Davis to apologize for anything Davis could prove wrong in the book and then make a correction in subsequent editions. Davis, he says, never took him up on it. "To this day, I stand by the book," says Hauser.

"I don't remember that offer," says Davis. "And that's not generous at all when he's gone through the paperback and hardcover editions. What good is [a correction] for a possibly nonexistent next edition? I remember him making a challenge."

The movie premiered a year ago, and Davis said it has taken that year for all three plaintiffs to make a collective decision to sue. The other two plaintiffs are out of the country -- former consul Frederick Purdy is now head of the U.S. consular section in Brasilia and Capt. Ray E. Davis (ret.) is in Santiago

"They feel very strongly about it," says Nathaniel Davis. "It isn't just my interest."

The suit says Ray Davis is the model for the character named Ray Tower in the movie. He is portrayed as a lecherous military official who tries to make a pass at Charles Horman's wife one evening while she is taking a bath. The characterization has apparently brought Ray Davis some unwelcome attention from embassy personnel in Santiago when Davis has business at the embassy. "I think he said they snicker and giggle," says former ambassador Davis. "He's pretty deeply unhappy."

Nathaniel Davis said he considered suing when Hauser's book, originally titled; "The Execution of Charles Horman: An American Sacrifice," appeared in 1978, "but... it's a big decision and it's also a big decision if you're not wealthy," says Davis, who makes $58,500 a year as a Foreign Service officer. "Eleven of us were, in fact, sued first by the Hormans." That suit was dismissed in 1981 without prejudice, which means it can be brought again. Edmund Horman said last year he requested the dismissal because government documents important to the case had been withheld.

"At that point we were being represented by the attorney for the Justice Department," says Davis, "and this attorney made it clear to us that although he would assist us in defending ourselves against the [Horman] suit, in any action we might take, the U.S. government was not prepared to involve itself."

Asked how he feels about this lack of legal support, Davis says, "I'd prefer not to comment on that."

The post-Allende Santiago of the Costa-Gavras film was one of grim chaos -- soldiers in tanks rolling down boulevards, bloodied and mutilated bodies lying at the curbside, a flash of a white horse galloping wildly through the city.

"Well, I didn't see the white horse running down the street," says Davis. "There were a lot of guns going off." But he did see bodies in the streets. A couple of blocks from the Moneda, the presidential palace, which was being bombed, embassy staff blocked the windows with mattresses.

"If you get someone like Costa-Gavras trying to depict this, the image you get is of utter butchery," says Davis. "If you get right-wingers, on the other hand, they'd like you to think Costa-Gavras' image is an utter, vivid lie... My image is not embracing either extreme."

Davis says the first time he heard of Charles Horman was when a consular official informed him of a telephone call from a Horman friend. Two people who knew Horman had received mysterious phone calls from Chilean military intelligence and relayed them to the embassy.

"I took all kinds of actions in trying to find him," says Davis, "and bear in mind that he wasn't the only one we were concerned with. How many were missing or known to be picked up by the military? About a couple dozen."

Davis says he even went to the new head of the Chilean government at one point. "I personally carried the inquiries all the way up to [Gen. Augusto] Pinochet," says Davis, who recalls discussing a number of items of business during his visit with Pinochet. "I asked him about both Charles Horman and Frank Teruggi [another American picked up by the military and later found dead]. He said he'd do his best to find out."

Hauser comments that that's the first time he's ever heard Davis mention going to Pinochet.

What Davis finds especially stinging is a scene in the film that is cited in the suit:

Horman: What is your role here besides endorsing a regime that murders thousands of human beings?

Ambassador: Let's level with each other, sir... This mission is pledged to protect American interests, our interests, Mr. Horman.

Horman: They're not mine.

Ambassador: There are over 3,000 U.S. firms doing business down here and those are American interests. In other words, your interests. I am concerned with the preservation of a way of life.

Says Davis: "... I'm depicted having a set of values in which I'm perfectly prepared to order or acquiesce in the killing of an innocent American in order to defend some business interests. That scene talks about 3,000 businesses doing business in Chile. That's nonsense. You could count the number of U.S. businesses in Chile in September of 1973 on your fingers."

The Chilean government now says officially that Charles Horman was found dead on a street in Santiago and delivered to the morgue on Sept. 18, 1973.

Davis has not been back to Chile since 1973. A year ago, when he appeared on "Good Morning, America" with the Hormans for a discussion of the film, Edmund Horman refused to appear on the same screen with him. Instead, Davis sat on one side of the set for his interview with host David Hartman. On another side of the set, Edmund and Joyce Horman sat for their interview with Hartman.

"As best I know, Charles Horman was dead when those phone calls [to the embassy] were made," muses Davis. "Now, if that's true, there's not a thing in the whole world we could have done. Now, I suppose in a sense that's a consolation for the successes and failures we had." He pauses. "I suppose I have a little bit of hope that if he had been alive, we could have found him."