The Haley family, by now one of the best-known in the United States, turned out in force last night to see its ancestors on the screen at the Eisenhower Theater.

Attending a VIP preview of "Roots: The Next Generations," to be shown on ABC-TV next month, Alex Haley, his two brothers George and Julius, and other relatives saw the first episode of the long "Roots" saga featuring people they had actually known -- the author's grandmother, and his great-aunt Elizabeth whose star-crossed love as an 18-year-old dominated the first episode.

The Haleys generally agreed that they liked the story, but felt uncomfortable about seeing their relatives portrayed by actors.

"I appear at four different ages in these seven episodes," said Alex Haley, "as an infant, at the age of 10 or 11, when I'm 22 and in the service, and finally when I am portrayed by James Earl Jones. And when I see myself on the screen, I can't help feeling: 'He don't look like me -- he don't act like me.'"

At a cocktail reception before the preview, and in the Kennedy Center atrium afterward, knots of admirers and autograph-sekers clustered around the celebrities present -- including Henry Fonda and Debbi Morgan, who have major roles in the first episode, and Elizabeth Taylor Warner, Sen. John Warner and Mayor Marion Barry.

Debbi Morgan, who ages from 18 to 80 in the six episodes in which she appears, spent a lot of time talking to members of the Haley family about Aunt Elizabeth, whom she portrays. "They told me that she used to dye her hair," Morgan reported. "When I get old in the series, my hair turns white; I guess that's because I'm so young they felt they had to give me white hair to help me look old.

"Now all my friends think I must know what I'm going to look like when I'm 80 years old, but all I really know is what the makeup artist thinks I should look like at that age. He gave me a double chin, for example, and I don't know whether I'll have a double chin. But I guess I have a better idea of how I'll look at 80 than most young people do."

The episode shown last night was set in 1882 in the town of Henning, Tenn. -- too long ago for anyone now living to remember what it was like. But Julius Haley used to spend his summers there as a child with his grandmother and great-aunt, and he was impressed by how well the town is captured on the screen.

"That's the town, all right, and that's the house the way I remember them. Of course, I knew my grandmother and great-aunt at a much later date than that, and I can't really relate them to the teen-age girls we saw on the screen tonight. The only places where I have real trouble are in the later episodes, where my father comes on. I can't get used to an actor playing my father. I say to myself. 'Yes, that's what he did -- but that isn't him doing it.'"

David Haley, a nephew of the author, was less serious when he said he has his part all cast in case the series ever gets down to a time where he might become part of the story: "I want O. J. Simpson," he said. "I won't settle for anybody else."

One Haley who appears in the series is the author's niece Anne, a student in Washington who plans to be a psychiatrist but doesn't mind doing some acting on the side.

"My name is Anne Shaw in the movie and I'm a friend of my grandmother's at Lane College," she said. "Some people get confused when I tell them that. I get one line in the third episode -- and they made me wear those pointed 19th-century shoes for one scene where I spent the whole time sitting at a table and nobody ever saw my feet."

When the book was published, and even more when the first "Roots" series appeared on television, Anne Haley recalled, her status was suddenly changed. "A lot of people who never paid much attention to me before all of a sudden became old friends. Some of that is nice, I guess, but you have to learn who is really your friend and who isn't."

Her brogher David recalled a feeling of relief when the book was finally published after years of work. "I didn't have to read it." he said. "It was as though I had already read it about 40 million times."

Standing in a quiet corner among the 300 guests at the cocktail reception was James B. Rhoads, archivist of the United States, who had been the host of the preview showing of the first "Roots" series at the National Archives.

"We had a tremendous surge of interest and a lot of activity after the first 'Roots' came out -- unfortunately without any increase in staff."

The National Archives have custody of "approximately 2.5 billion pieces of paper" as well as a lot of microfilm, he said. "We have a lot of military records and even records of ship arrivals and passenger lists. If you know what ships your ancestors arrived on and when, or what regiments they served in during, say, the Civil War, we can probably find a reference to them."

Records on black families before the Civil War are relatively scarce, he said, "at least in the National Archives. Church records and local courthouses are useful sometimes -- but so many churches and courthouses have burned down."

Another Washington institution that has seen increased attendance as a result of "Roots" is the Museum of African Art, according to its director, Warren Robbins, who was at the preview. "It helped to remind people that Americans aren't all simply transpllanted Europeans," he remarked.

The hundreds of guests who sipped cocktails and chatted for an hour in the Eisenhower Theater lobby before the preview, dined afterward on roast beef, potatoes, and endive salad.

The Haley family, now solid members of the professional class (one brother is an attorney, the other an architect), moved with ease through the gala surroundings of the Kennedy Center atrium, and may have enjoyed it all the more after a graphic, two-hour-long reminder of the humble soil their roots grew in a century ago.

"The best part of it," mused Anne Haley, looking around the festive room filled with people drawn there by the story of her family, "is how Uncle Alex has stayed unchanged. He's still the same sweet person he was -- a lot richer, but basically unchanged. The only time you notice any difference is at Christmas, and I don't mind that at all."