GEORGETOWN'S BIOGRAPH theater winds up its six-week tribute to Francois Truffaut on Christmas Eve with the French director's final film, Confidentially Yours, completed several months before his death last year. The comedy-thriller screens Friday through Tuesday with his 1981 The Woman Next Door.

On Christmas Day, the Biograph begins its "Down Under Festival" of the films of Australia and New Zealand, which runs to the first week of March. It opens with the Washington premiere of Utu, which has been described as "a sort of New Zealand Western."

Some of the better-known movies in the festival include The Year of Living Dangerously and Breaker Morant (both scheduled for January 17 to 20); and two Mel Gibson flicks Mad Max Beyond Thunderdome (January 31 to February 3) and Gallipoli (February 4 to 6). Silver City, nominated for 11 Australian Academy Awards, will have its Washington premiere on the bill with "Gallipoli."

The theater is importing Australian candy and will also offer hot Australian meat pies and hors d'oeuvres on Thursday evenings during the festival. Call 333-2696.

Circle Releasing Company, an 18-month-old local film distributor that hit it big with Blood Simple, is now back with Letter to Brezhnev, which will have a sneak preview Saturday at 8 at the Outer Circle. The British comic love story, a big hit in London, stars Peter Firth and Alexandra Pigg and Margi Clarke, two actresses popular on English television.

Written by Margi Clarke's brother Frank, the film is the story of two Liverpudlian lasses who fall in love with a couple of Russian sailors and the complications that follow.

Roth Theaters, which operates 32 screens at 14 locations, reopens its three Village Mall Cinemas in Gaithersburg on Friday after spending more than $100,000 on new projection and sound equipment, screens, seating, lighting and floor resurfacing. The theaters will be showing Back to the Future, Out of Africa and Enemy Mine. Call 948-9200.

In Rockville, Roth's Manor Theater has invited Santa Claus to pass out candy canes to kids, and information about pet adoption to their folks, before the first two screenings of Walt Disney's 101 Dalmatians on Saturday. The activities will run from 11:40 to noon and 1:30 to 1:50. Sponsors are the Montgomery County SPCA and the Greater Washington Dalmatian Club, some of whose members will display their champion dalmatians and puppies. Call 460-1222.

REMINDER: The American Film Institute will be closed from this Friday through next Thursday, reopening December 27 at 6:30 with a tribute to "Celluloid Sleuths: The Literary Detectives on Film Part 1 -- Hollywood Gumshoes." The series begins with a coule of Humphrey Bogart greats, The Maltese Falcon and The Big Sleep.

SHORT SUBJECTS -- "The War Film" series finishes out the month Friday at noon at the National Archives with a showing of the 86-minute Sun Valley Serenade. Glenn Miller made his film debut in the movie, which also features Milton Berle, Joan Davis and Dorothy Dandridge. It's free, at Pennsylvania Avenue and Eighth Street NW . . . Later Friday, at 7:30, the National Air and Space Museum continues its "Comet Tales" series in the Langley Theater with the 1963 Howard Keel "drive- in-movie" thriller, Day of the Triffids. (The series' next screening will be January 3 with Rocketship X-M . . . Fans of Scrooge can see the 118-minute, 1970 remake starring Sir Alec Guinness, Albert Finney and Dame Edith Evans on Saturday at 1 in the Mary Pickford Theater at the Library of Congress. It's free, but reservations are advised. 287-5677 . . . There's still time to catch Miracle on 34th Street. The realtors at Century 21 United of Falls Church are sponsoring a screening Sunday morning at 11 at the NTI Annandale. It's free, but bring a can of food for the needy . . . The Japan Information and Culture Center's free lunchtime series screens Hiroyuki Iwaki, the story of a conductor, on Monday and Tuesday. On Thursday and Friday see Japanese traditional musicians in Tagasu Den and the Odenkoza. All screenings are at 12:30 at 917 19th Street NW. Call 775- 0847/0848 for details.