THIS IS NO TIME for the great outdoors, people. The National Gallery of Art, the Corcoran, the Library of Congress, The American Film Institute, National Air and Space Museum, American University, the Hirshhorn and many others -- as usual -- are showing flicks galore. The films are free unless otherwise noted.

The restored print of Sadie Thompson, Raoul Walsh's 1927 film starring himself, Gloria Swanson and Lionel Barrymore, will be shown at the Hirshhorn Friday at 8. Dennis Doros, who was instrumental in "Sadie's" restoration, will introduce it. 357-2900 . . .

This weekend at AFI it's My Son John (Friday and Sunday at 6:30), Leo (Duck Soup) McCarey's now-campy anticommunist drama with our own Helen Hayes and Dean Jagger. Also the finale of the Latin American Film Festival, with Marcos Zurinaga's La Gran Fiesta (which had an all-too-brief run here recently) and Kevin Conway's The Sun and the Moon, Friday and Saturday at 9. There's also a chance to see both Alien and Aliens together, Saturday at noon and Sunday at 1:30. And Lina Wertmuller's "fantapolitical" A Joke of Destiny (Scherzo) has its D.C. premiere Wednesday and (next) Friday at 6:30. It's $4.50 for nonmembers. 785-4600 . . .

This Friday at 7:30 Air and Space will show (for $1) Firefox in 70mm, with Clint Eastwood as an ace NATO pilot who must commandeer a Soviet plane. Coming up in this "Aerial Pursuits" series (same time and place) are Command Decision (1948) with Clark Gable (Friday October 30); as well as Catch 22 (November 6); The Red Tent (November 13), The Court Martial of Billy Mitchell (November 20) and Top Gun (December 4; this also is in 70mm) . . .

Saturday (2:30) and Sunday (at 6) at the National Gallery's East Building, it's Vincente Minnelli's Lust for Life, starring Kirk Douglas as Vincent van Gogh . . . Also Saturday (10:30 a.m.) at the Corcoran, Los Sures, a one-hour documentary on the Puerto Rican community in New York, as well as Low 'n' Slow: The Art of Lowriding, a half-hour film on the customized-vehicles culture . . .

The "Images of Vietnam: The Struggle for Memory" series continues with Tuesday's double bill of Joseph Strick's Interviews With My Lai Veterans and Emile de Antonio's In the Year of the Pig. Both Strick and Antonio are scheduled to appear. The 8:45 show's at the AFI; $5 general admission. Thursday night at 8, Wayne Ewing's The Bloods of 'Nam will screen in the lecture hall of the new Quadrangle Building (enter at the Mall kiosk). There to answer questions will be Wallace Terry, who adapted his book "Bloods: An Oral History of the Vietnam War by Black Veterans" for the film. Admission is $5 for Smithsonian Resident Associates members, $6.50 otherwise. 357-3030 . . .

Monday at American University's Wechsler Theater, it's Jacques Tourneur's Out of the Past (5:30). Tuesday at 5:30, Polish director Krzystoff Zanussi's A Year of the Quiet Sun; Wednesday, 5:30, Walsh's 1940 They Drive by Night and at 8:10, a Jayne Mansfield special -- The Girl Can't Help It. 885-2040 . . . Zanussi's "Sun" will show again at the Reston Community Center Theater November 22. Tickets may be obtained at the Northern Virginia Community College's Loudoun campus. 476-4500 or 450-2571.

And next week, look for the Library of Congress' showing of the first 10 Oscar- winning pictures, 1927-1937.