ALTON TRUMBO, the Hollywood screenwriter, once said that during the blacklist period of the late '40s and early '50s there were "only victims." One would be tempted to say the same thing is true in "Missing," the Costa-Gavras picture telling of the 1973 Chilean execution of a young American named Charles Horman, if it weren't for one exception. Universal Pictures, which opened "Missing" a little more than three weeks ago in seven theaters around the country, is slightly astonished to discover that it is that Hollywood anomaly--a political picture whose grosses are, Variety said last week, "heavy," "smash," "incendiary."

"In its first 13 days in those theaters," said Gordon Armstrong, a Universal Vice President in charge of marketing and advertising, "we brought in $500,000. And those were small theaters. Three hundred seats in San Francisco, 500 New York, 300 in Boston," he said. Friday, they "open wide."

When Universal opens wide, it means 600 theaters, and Hollywood will discover whether or not America will buy a picture whose story its government disavows, one of the few commercial, overtly political films to come out of the industry since the Vietnam era ended. "We were confident," Armstrong said, "but not overconfident. It was, we were sure, a movie people can relate to on a human level. If it was just a political film, it would go down the toilet quickly."

Hollywood will work hard to nail "Missing's" good business to its human and not its political strength. Nevertheless, in the weeks since it has opened, it has drawn good reviews, torrential controversy, the committed attention of both mainstream and alternative press, the deep interest of ideologues and former State Department employes around the world. It has attracted classical arguments between factions forming on the sides of Art and Truth on the matter of their connecting tether--and yet there are victims all over.

Surely, the Horman family are victims, and surely some Chileans were as well. Former U.S. ambassador to Chile Nathaniel P. Davis says there is another kind of victimization. "What I saw in the picture never happened," he says. "The scenes that were shown may have existed in someone's mind but I don't remember them."

In the case of Edmund Horman, father of Charles Horman who searched for his son through civil strife and against what he calls an unresponsive American embassy, it brings memories and emphatic statements of "Missing's" veracity.

In the days following the September 1973 coup in which Salvador Allende's socialist government was felled, Charles Horman, 30, disappeared.

On Oct. 4, 1973, Edmund Horman went to Santiago from his home in Manhattan to search for his only son. That search is the subject of "Missing." It is a story based on a book by Thomas Hauser, a story with which the State Department has already taken issue, in the form of a rare formal statement just prior ot the film's release.

That statement said in part, "The Department of Stateundertook intensive and comprehensive efforts to locate Charles Horman from the momentthat it was learned he was missing, to assist his relatives in their efforts to locate him, and also to learn the circumtances of his disappearance and death . . . Theseefforts continued for eight years and involved many special investigations, cooperation with other agencies and included an internal investigation of the possiblity that U.S. government officials might have initiated, condoned or failed to act effectively in Horman's disappearance and death." The statement said those investigationsrevealed nothing about Horman'sdisappearance.

To that, Edmund Horman has said, "The thingsthey're saying are practically word-for-word untrue."

"Missing" tells of Horman groping through the junta's machinery before finding--after a two-week search--that his son had been killed two weeks before Edmund Horman even reached Chile, had been buried in the wall of the National Stadium just the day before. He undertook the search with Charles' wife, Joyce. He says he learned of the death through an underground source. He says he had to have his brother-in-law tell his wife, Elizabeth, because he could not.

Horman believes that his son was killed because he became witness to disclosures regarding American assistance in the coup. While traveling with another American, Terry Simon, he had run into U.S. military personnel and they reportedly spoke openly with a fellow American about their participation in the coup. Charles Horman listened, and soon after he was dead.

Charles Horman had been a literary son with an independent mind. He was sent to the Allen-Stevenson School in Manhattan, and to Exeter and to Harvard where he graduated magna cum laude. He got a Fulbright Scholarship. When he graduated from Harvard, Vietnam was just simmering and Charles worked off his service requirement in the National Guard. In the '60s he protested the war, was maced in Chicago and worked for the federal poverty program as a historian. In 1968, he married 24-year-old Joyce Hamren (who is called Beth in the movie), and the two traveled throughout South America. When they reached Allende's Chile--with its leftist dreams--Charles Horman told his wife he had found a place where he could write, that he had found himself.

Almost 10 years later, Edmund and Elizabeth Horman are still articulate, strong, separate forces. He is an industrial designer. She paints professionally. With one exception her scenes are filled with sunlit pastels. These paintings hang in the Manhattan apartment in which they've lived for 40 years, along with photographs of Charles as a boy, a college freshman, a new husband.

Edmund Horman sits in his living room wearing a jacket with his wide tie knotted over a Lacoste shirt buttoned to the neck. Since 1973, he has compiled a fat sheaf of documents not only to demonstrate his search for the truth behind his son's execution, but to back up his belief that execution was covered up by the American government.

Hunched over his own coffee table, he goes through page after page of correspondence and of court orders, of diplomatic documentation, State Department memos, official concessions and official disavowals. Edmund Horman knows all of it by heart. He brought suit against the United States government (Horman v. Kissinger, et al.) in 1977 in the matter of his son's murder. Horman said he had to drop the case when he couldn't get the government to release what he terms essential documents. But the State Department contends that the unreleased documents do not pertain to the case but only to classified aspects of U.S. foreign policy. The suit was dismissed without prejudice last year.

"In the beginning," Ed Horman said, "I figured the Congress would rip the cover off it and buggy-whip whoever was responsible. One member of Congress said, 'If I never do another thing, I'll take care of this.' Well, it didn't quite work that way . . ."

"They never expected to be pushed," he says, "I think they just thought it would go unchallenged. They kept on trying to tell me that Charles was in hiding, that he had had to go into hiding and would probably turn up. This supposed, of course, that he was a leftist and had some reason to hide. He didn't. And it was a ridiculous story. He would have called somebody he knew--he knew a great many people--and he would have said, 'I'm hiding in an ashcan behind a car.' But the embassy kept insisting, and it was a very short time after I got down there that I knew they were lying to me."

"I was surprised in the beginning," he says. "They gave me a car and a chauffeur and all the help I needed. I got in touch with some people to find out what the facts were and then--day after day I was told they had to report they hadn't found anything. And then I came to believe they knew but they just weren't telling me anything. When I went down there I was like a lot of Americans and I just expected our government to tell the truth to protect its citizens. It didn't take me long to find out that that year in Chile that wasn't the case."

"Ed can be a very forceful man," Elizabeth Horman says. "And he stumbled into some things that he wasn't supposed to."

Edmund Horman smiles for the first time. "I had mentioned to one of the embassy aides that I knew there was an undercover system of getting information, that I had read about what had happened in Uruguay where our channels had shown up, and that afternoon I got a phone call from that aide to come down and see the ambassador. 'The ambassador would like you to come over right away,' " Horman remembers.

Horman tells of that meeting with Davis: "I came down, and he was sitting on a big overstuffed piece of furniture. 'I understand,' he said, 'you want to discuss some political affairs.' I was taken aback. I had no idea what he was talking about. 'I understand,' he said, 'you made some reference to some kind of police assistance program.' I told him I had. The ambassador looked at me. 'We don't have anything like that,' he said. I think he assumed if he said we didn't have any program like that, I'd say 'yes sir' and that would be that.

"But what I said to him was, 'I'm only down here for one thing--to get my son back.' "

"You're powerful," Edmund Horman says he told Davis. "I know you can pick up a phone and find out what happened--I'm only asking you one thing: Don't ask me to go back to my wife and tell her I don't know what happened."

In the weeks since "Missing" has opened, there has been a great deal of controversy over whether or not the American Embassy and its staff obscured the known facts of Charles Horman's death. Former ambassador Davis was called by the staff of "Good Morning America" a couple of weeks ago and asked to watch the picture. He did, and "it brought back the tragedy of the time," he says, "the tragedy of the Chileans, the tragedy of the Horman family losing their son. It is also said that a bunch of perfectly honorable officials are being accused of murdering him. That sadness is nothing compared to the sadness of parents losing their only boy, I know. I'm not trying to compare them. I have every sympathy for the Horman family. But I'm also a little sad they're treating us quite the way they do."

The ambassador is portrayed in the picture as benign on the surface but with sinister imperialist undertones. He appears both kindly and obstructive. The scene Horman describes, crucial to the movie, in which Horman is called into the ambassador's office just to be told that there is no American participation in local security matters--no "police assistance program"--Davis says, speaking from his home in Rhode Island, "never happened. I certainly didn't tell him that there was no CIA station; that would be a silly thing to say. I'm not sure what kind of program the movie was referring to--one thing I can be perfectly sure of that Edmund Horman won't believe, but is true: I myself did not lie to him. I was honest with him. If he suggests I called him in to lie to him, I know I didn't do that. And in fact, if Ed Horman was asking me about the public safety advisory program that had existed for security reasons, well I don't believe it existed anymore in 1973.

"If the picture is saying that our embassy officials were accomplices in Charles Horman's murder, it is wrong. If it is saying that the American Embassy was plotting and carrying out the coup--it's not true. It is true there were several Navy officials stationed there, but that was just their post of duties.

"Some of the press accounts have asked why Charles Horman was killed, and the picture tries to say that he was killed because of what he knew about American participation in the Chilean coup. Let me say that if Charles Horman was fingered, why was not Terry Simon--the woman . . . with him who was privy to the same information--rubbed out also? If the United States government decided to rub out Charles Horman, why is it that nothing happened to Terry Simon?

"Nobody is accusing the United States government of having been complicit, of having fingered the three nuns who were murdered in El Salvador. Why are we being accused of complicity here? It doesn't hold water. When a coup is going on and all the lot is unstuck, things happen. I don't see the rationale that says if he died we had to know about it. There were a lot of things going on they didn't consult us about.

"They went through all his papers. It's possible they found something in his papers that set them off, that made them angry.

"And as far as telling Ed Horman about his son, as soon as we got any information in our pipeline, we passed it on. It was represented in the movie we were trying to tell lies. I don't understand how we were supposed to hide information or what our motives were supposed to have been."

Says Judd Kessler, a former embassy aide who is now a counsel to the State Department, "The Chileans certainly had their reasons for not wanting this whole business to get into the press at the time. I'm not trying to defend what they did, but the charges against our ambassador and our personnel are disturbing. Nat Davis is as fine a person as there is, and he's not a right-wing character either."

Looking back, Horman remains adamant in his criticism. "They thought Charles was dangerous anyhow. Then he had heard about American activities in the coup. That made him a very dangerous man. They had him designated on his dossier as a journalist and a leftist. Our government were the ones that were keeping information on him. The Chileans seized him.

"If you accept the fact that the whole business of getting rid of Allende was in the interest of the multinationals, and that was the reason for the coup, it makes sense we were involved. It was an American interest. And Charles' murder happened around the same time that Kissinger had been nominated for secretary of state. And the government did not want anything raised that would make things difficult. There were a lot of people who wanted to see the facts brought out, but nevertheless they were covered up.

"We fought for a long time to have those facts brought out. We lost a lot of friends--people thought we were crazy, or people thought we were Communists. Maybe the film vindicates us a little. I fought for attention all those years. Now we've gotten it and maybe we'll get the truth."

Horman pierces the conversation with his allegations, and yet: his eyes glisten, the hardness is transitory, and when he speaks of his son he smiles despite himself. He stands up next to his wife in the big living room. Elizabeth Horman leads the way up a step and begins walking through the apartment, pointing out pictures of Charles as he grew older and became a man. She points out the table at which Charles sat after his first Chilean sojourn, where he sat and described the political turmoil of the country to his parents. She tells how his body wasn't returned for seven months after the coup. She steps up to her studio and shows her one painting in the house not filled with sunlight and flowers and colors: It is a painting of Santiago after the coup and the murder. She smiles slightly while she talks about her son, whose picture, forever young, smiles back from a table in the living room.

She asks a visitor sitting near her how old he is. Thirty, she is told.

"Oh," says Elizabeth Horman, smiling, with a distant look in her eyes, "that's how old Charles is."