CELEBRATING the completion of its new eight-theater complex at the Beltway Plaza in Greenbelt, American Multi Cinema Inc. will offer an open house there Thursday evening.

Along with free screenings of JoJo Dancer, Blues City and Critters at the just-built Academy 8, there'll be mimes, clowns and free popcorn, sodas, hot dogs and movie passes. The fun begins at 7 p.m. For details, call 220-1155; for a job, call 220-0022.

When the new complex officially opens the following day, AMC will have pushed its total seating capacity to more than 3,500 at 14 screens in Greenbelt alone. The addition of the Academy 8 is part of a plan to nearly triple the number of AMC screens in the Washington area by the end of the year.

The Kansas City-based chain -- which also operates the Academy 6 at Beltway Plaza, the Skyline 6 at Baileys Crossroads and the Carrollton 6 in New Carrollton -- invested more than $4 million in the 2,000-seat eight-plex, which is less than a hundred yards from the 11-year-old Academy 6 theaters.

Theater architects have used a mauve-and-grey, brass-and-chrome look in the auditoriums and spacious lobby. A computerized ticket booth will allow tickets to be sold in advance.

But more importantly, AMC has fulfilled its earlier pledge to build wider auditoriums with larger screens, getting away from its former design of long, narrow theaters with tiny screens. Two of the new theaters will be capable of showing 70mm films, complete with a state-of-the-art 25-speaker stereo system. All theaters will have stereo surround sound and seating for the handicapped.

AMC, which last year reported more than $240 million in ticket sales at 975 screens, is working on an ambitious expansion plan that calls for opening 325 screens nationwide over the next 18 months. On June 23, AMC will open a 2,400-seat, 10-screen complex at Potomac Mills in Woodbridge and recently began construction on a 2,700-seat, 12-plex at Rivertown in Oxon Hill, which is scheduled to open in December.

Meanwhile, bulldozers are at work at the site of the old Lee Highway Drive-In, where Redstone Management of Dedham, Mass., plans to open a dozen theaters this fall. Construction is also under way at the old Mount Vernon Drive-In, where the theater company expects to open a ten-plex, also this fall. Redstone has owned and operated theaters at both sites since the 1940s.

The Museum of American History continues its topnotch review of 70 years of Hollywood this Saturday at 1 in Carmichael Auditorium with "All Talking! All Singing! All Dancing!," a lecture by Carl Scheele, curator and culture historian in the Smithsonian's Division of Community Life.

The hour-long event coincides with American History's "Hollywood: Legend and Reality" exhibit, which includes more than 450 photographs, posters, costumes and such props as Citizen Kane's "Rosebud" sled, the miniature models used in making "King Kong" and "E.T." and the piano in Rick's Cafe from "Casablanca." The exhibition runs through June 15.

At 2, also in Carmichael Auditorium, see Harry Beaumont's Broadway Melody, awarded Best Picture in 1929 and starring Bessie Love, Anita Page, Charles King and Jed Prouty. This 104-minute production is one of Hollywood's first talkie musicals and was scored by Arthur Freed and Nacio Herb Brown. All events are free. For information, call 357-2700.

It appears that Hollywood is growing closer to Charlottesville all the time. Actors Sam Shepard and Jessica Lange recently purchased a spread in Albemarle County, but details of the sale are being kept private. In making the move East, Shepard and Lange, who made Country together, join such other celebrity farmers as Sissy Spacek and her director husband Jack Fisk; novelist and screenwriter Rita Mae Brown; and billionaire broadcaster and producer John Kluge, who owns Metromedia Inc.

Although no real estate agent has claimed or confirmed the sale, several colleagues said that the Roy Wheeler Co., a longtime dealer in historic properties and luxury estates, dealt with a representative of the couple.

Some believe that celebrities move to the Charlottesville area to escape the Hollywood hassle.

"They just want to be normal people," figures Frank Quayle of the Wheeler firm. But Quayle says the celebrities aren't attracting other stars. "They wince when they hear that other ones celebrities are here."

In late February, actor-singer Wayne Newton, who runs one of the nation's largest Arabian horse breeding farms outside Las Vegas, backed out of a contract to buy the 1,180-acre Castle Hill estate near Keswick, less than 10 miles from Charlottesville.

The Bethune Museum and Archives will sponsor a panel discussion, "A Second Look at the Color Purple," on Sunday at 3, part of its continuing lecture series. Washington Post reporter Jacqueline Trescott is the moderator for a group that includes David Nicholson of the Black Film Review and Calvin Forbes, professor of English at Howard University. It's free, at 1318 Vermont Avenue NW. Call 332-1233.

Fans of animation won't want to miss "The Films of Sally Cruikshank" on Tuesday at the American Film Institute. The 80-minute program presents all nine of the Berkeley-based filmmaker's works, including her 1971 debut piece Ducky. Also scheduled are Fun on Mars (1971), Chow Fun (1972) and Quasi at the Quackadero (1975). For tickets, call 785-4600 or 785-4601.

On Wednesday evening, the Biograph Theater opens the 19th International Tournee of Animation. Over the next 15 days, the Georgetown movie house will offer 20 of the most honored animated films. Among them are this year's Oscar-winner for Best Animated Short, Anna and Bella, from the Netherlands; last year's winner from Canada, Charade; and another Canadian production, Anijam, which won the Toronto Animation Festival's Special Jury Award. "Anijam," which is just over 10 minutes long, is an amazing collection of drawings produced by 22 artists who were each given a 15-second segment to display their craft. Tickets are $3.50. Call 333-2692 for a complete screening schedule.

SHORT TAKES -- American University's Media Center and the Washington Chapter of the National Academy of Television Arts and Sciences on Friday will sponsor the screening of two black-and-white movies by local filmmakers at the Mary Graydon Center.

One State, a slick 32-minute futuristic spoof by Bruce Cooke and Douglas Painter, begins the evening at 7:30. The film received an honorable mention at this year's "Expose Yourself" festival at the Biograph. Andy Zmidzinski's 50-minute Persistence in Vision, the story of a young artist haunted by a girlfriend's sudden death, will also be shown. Zmidzinski will answer questions after the program. A donation of at least $2 is requested; a reception follows. Call 885-2040 or 587-3993.

The AFI offers a pretty strong box office schedule this weekend with the first Rocky on Friday at 6:30 followed at 8:45 by Gold Diggers of 1933 double billed with 42nd Street. On Saturday at 6, see Orson Welles' Citizen Kane. Call 785-4600 or 785-4601.

Washington filmmaker Pamela Peabody's Dorothy Hood: The Color of Life gets its local debut this Sunday on WETA-TV Channel 26. The 30-minute documentary traces the 66-year-old Houston painter's career. Former Washingtonian Carl Colby, whose father William Colby is a former director of the CIA, is the film's co-director. The program airs at 4:30.