THE FOURTH Americas Film Festival begins Saturday at 7:30 with the Venezuelan film "Aventurera" and concludes Oct. 30 with a second showing of the Brazilian production "Stelinha" (also shown at 9 Oct. 26). In between are 20 other films from Ecuador, Venezuela, Canada, Brazil, Puerto Rico, Colombia, Spain, Mexico, Haiti, Jamaica and other countries.

The festival also includes "La Luna en el Espejo" (at 7 Oct. 27), a Chilean film for which Gloria Munchmeyer won the Best Actress Award at the 1990 Venice Film Festival. Munchmeyer and the directors of all 22 films are scheduled to attend the festival.

Admission for all films is $6 ($5 for AFI members). For more information, call 202/828-4093.

AT 8 FRIDAY at the Hirshhorn auditorium, filmmaker Arthur Dong will introduce his "Forbidden City," part of the Asian American Film Festival. Admission is free. At 8 Thursday and Oct. 26, the Hirshhorn will also screen "Tabu," the 1931 classic filmed in the South Pacific by F. W. Murnau and Robert Flaherty. This will be its first theatrical showing in 40 years.

ON SATURDAY, the National Gallery of Art opens "Soviet Cinema in Transition." The series shows the work of six prominent directors, most of them graduates of the Russian State Film School, and kicks off with Vadim Abdrashitov's 1988 "The Servant" at 1:30 and his 1984 "Parade of the Planets," shown at 6. The films are free and shown at the Gallery's East Building auditorium.

"MUSIC IN the Movies" is this year's theme at the third Virginia Festival of Film. It begins at 8 Wednesday at the Charlottesville Performing Arts Center with a screening of "The Thief of Bagdad," which "Bagdad" star Douglas Fairbanks Jr. will attend.

Director George Sidney and singer-actress Kathryn Grayson are among the other stars and filmmakers who'll attend the festival, which concludes Oct. 28. The event will feature more than 100 screenings, including a tribute to Sidney. Call 800/882-3378 or 804/924-3378.