SATURDAY afternoon at 2:30, the National Gallery of Art will screen Greek filmmaker Theodor Angelopoulos' 1975 film Travelling Players (O Thiasos) at the East Building (Fourth and Constitution NW). "Players" is a highly expressionistic film, characterized by long takes, about a troupe that performs one play, "Golfo The Shepherdess," over the period 1939-1952. During that time, they encounter the Nazi occupation of Greece as well as the bloody civil struggle that culminated in the 20-year series of right-wing regimes. And there is a subplot loosely based on Aeschylus' "Oresteia." Angelopoulos' film lasts 3 1/2 hours; there will be an intermission. Admission is free. University of Maryland communications professor Robert Phillip Kolker will introduce the film.

On Thursday, Donald Glut, an author of dinosaur books for children, as well as a dinosaur consultant/creator for animated television series and films, will give a lecture called "Lights, Camera, Action -- Dinosaurs and the Movies." The talk, sponsored by the Smithsonian Resident Associates, will be at the Museum of Natural History's Baird Auditorium at 7. With the help of film clips, he will talk about the depiction of the big prehistoric things in the movies over the years. Admission is $7.50 for non-members. Call 357-3030.

Premiere, a nonprofit support group for the American Film Institute, sponsors a fund-raising premiere of Emile Ardolino's Dirty Dancing to benefit the AFI Tuesday at 7:30 at the Circle Embassy. Afterwards, there will be a '60s dance reception at the Dakota nightclub in Adams Morgan. Director Ardolino, producer Linda Gottlieb, "Dancing" star Cynthia Rhodes and screenwriter Eleanor Bergstein are expected. Tickets are $25; $30 at the door. Call 785-4601. The film opens commercially August 21.

Friday at 7:30, at the University of Maryland's Center of Adult Education auditorium (University Boulevard and Adelphi Road, College Park), it's Otto Preminger's Laura; next Friday, same time, it's Joseph L. Mankiewicz' All About Eve. Admission for each is $3. Call 985-7000 . . . Fridayt at the Library of Congress' Mary Pickford Theater, George Sherman's Sword in the Desert, with Dana Andrews. Tuesday, it's Mankiewicz' People Will Talk, and Thursday, Alfred Hitchcock's To Catch a Thief. Both films star Cary Grant. All Library films are free and at 7:30. Call 287-5677 . . . Thursday at 7 (also free), the National Archives will show Preminger's Anatomy of a Murder at the Archives' fifth floor theater. Call 523-3000.