AFTER nearly two years in production, The Phillips Collection, a detailed historical documentary about Washington's famous homegrown gallery and its public- spirited founders Duncan and Marjorie Phillips, has opened at the gallery. The 40-minute video production, made by the New York-based Checkerboard Foundation, Inc., includes interviews with National Gallery of Art director J. Carter Brown, retired columnist Joseph Alsop, Washington artist Sam Gilliam and Washington Post Company Chairman Katharine Graham. The film also includes part of a January 1984 interview with Marjorie Phillips recalling the collection's beginnings. The release marks the 100th anniversary of Duncan Phillips' birth and the first anniversary of Marjorie Duncan's death last June at age 90. Free screenings are at 10:30 and 3:45 Tuesdays through Fridays, 10:30 on Saturdays and 5 on Sundays through August at 1600 21st Street NW. Call 387-2151 for more information.

The Capital Children's Museum offers a behind-the-scenes look at the making of the new Jim Henson and George Lucas film Labyrinth, in a special display open daily through July. The exhibit, at 800 Third Street NE, features montages, murals and props from the film including two new Muppet characters, Alf and Ralph. There's also a four-minute video that provides an insider's look at the film's production at England's Elmstree Studios. The museum is open from 10 to 5 and admission through Monday is $2 for adults and children. Beginning Tuesday, admission changes to $3 ($1 for those 60 and older, free for those under 2). Call 675-4123. ("Labyrinth" opens Friday.)

Advertising departments across the land found the provocative title "Sexual Perversity in Chicago" too hot to handle when Tri-Star Pictures tried to buy space several months ago, so the film company renamed the comedy About Last Night. The screenplay, written by Denise DeClue and former "Saturday Night Live" comedian Tim Kazurinsky, is based on the David Mamet play. It stars Rob Lowe, Demi Moore, Elizabeth Perkins and Kazurinsky along with another former "SNL" member, Jim Belushi. The picture opens July 2 but the American Film Institute is sponsoring sneak previews Tuesday night at 6:30 and 8:45. AFI staffer Gina Rogak -- who appeared in the original off-Broadway cast in 1976 -- will introduce the film.

On Wednesday night the AFI will sneak-preview the new feature A Great Wall at 6:30. The 102-minute Orion Classics release, billed as "the first American movie made in China," is the story of a San Francisco-based Chinese-American family's reunion in Beijing after a 30-year separation. Actor Peter Wang, who co-wrote and directed, will be joined by producer-screenwriter Shirley Sun following the screening for a question-and-answer session. The film is in English and Mandarin with subtitles. (It opens at Georgetown's Key Theater on July 11.) For a complete list of AFI showtimes and ticket information call 785-4600 (recording); or 785-4601.

With all the young, high school girls eagerly gathered outside the manager's office at the Uptown Theater on a recent night, anyone could easily have mistaken the scene for a visit by Tom Cruise, or some other teen idol.

"We are, like, two of his all-time greatest fans," swore Eileen Schmidt, posed as if for a courtroom oath. And she was not talking about Tom Cruise.

"We love Norman. We doooo!" cooed Susan Shannon.

Inside the office overlooking Connecticut Avenue was actor Tony Perkins, an unlikely teen-age idol, looking a little too sinisterly like Norman Bates as he prepared to introduce his latest film, Psycho III, to 700 invited guests.

The week before, Schmidt and Shannon rented Psycho and Psycho II on videotape in preparation for the premiere and got their parents to bring them in from Springfield to the special screening. But their folks weren't as tickled to see the picture.

"They weren't half as excited as we were," admitted Shannon. "They think he's a little strange."

You can decide for yourselves starting on Wednesday when the films opens nationally.

PBS television stations will begin the summer-long "American Playhouse Movie Festival" Thursday night at 11 with Philip Roth's best-selling story, The Ghost Writer, starring Claire Bloom and Sam Wanamaker. The films were first aired during the early days of "American Playhouse" and are rarely found on videocassette, and never on commercial television. The vintage productions will be seen locally on WETA-TV Channel 26 and contain some profanity but will run unedited. Among the scheduled films are The Europeans, starring Lee Remick (July 10); Testament, which brought Jane Alexander an Academy Award nomination as Best Actress (August 14); and The Ballad of Gregorio Cortez (August 7). Call 998-2626. FILM COURSES -- The American University Film & Video Institute begins its Fifth Annual summer program with sessions starting July 29 and August 5. The intensive "Production Master Classes" and "Post-Production Master Classes" are six-day courses (spread over an eight-day period) covering such topics as advanced location lighting, audio recording for film and video, on-line video editing, advanced film editing and more. Course costs range from $465 to $685. Call 885-2046. SHORT SUBJECTS -- The free "American Lives" series at the National Archives concludes its June programming on Friday with a noontime screening of the 1974 production, The Journey of Lyndon Johnson. The 48-minute film begins with the former Texas schoolteacher's first elected position in Washington politics in 1931 and traces his fascinating climb to America's most powerful office and examines his personal anguish over the Vietnam War. The Archives are at Pennsylvania and Eighth Street NW. Call 523-3000.

(Don't forget that the Smithsonian's ongoing 20th annual Festival of American Folklife will be offering free film screenings all weekend at Baird Auditorium in the Museum of Natural History. This year's featured topics are Japan, Tennessee and trial lawyers. For a complete movie menu, call 357-2700.) FILM HISTORY -- Ten years ago Friday, Palestinian extremists hijacked an Air France plane carrying 257 people on a Tel Aviv-to-Paris flight, had it refueled in Libya and ordered it flown to Uganda's Entebbe airport. The event inspired three made-for-television movies -- "Victory at Entebbe," "Operation Thunderbolt" and the above-average "Raid on Entebbe" with Peter Finch, Charles Bronson, Horst Buchholz, Martin Balsam, Jack Warden and others.

Baby Boomers take note: on Friday "Captain Kangaroo," a.k.a. Bob Keeshan, celebrates his 59th birthday.

Comedian-movie director Mel Brooks turns 60 on Saturday while actress-comedian Gilda Radner turns 40.