Residents of Peking are now better acquainted with their sister city Washington. For most of October, the Working People's Cultural Palace in Peking's Forbidden City displayed 97 photographs depicting the people, events, buildings and neighborhoods that make up Washington.

"We were looking for a variety of photographs which would express the many aspects of life in this city," said Barbara Ashbrook, chairman of the exhibition committee. She said that the collection was comprehensive, featuring shots of the elderly, the Redskins' mascot, a Little Tavern hamburger shop and even a life-size cardboard picture of President Reagan with which tourists often have themselves photographed. Ashbrook says that exhibition coordinators were a little concerned that some of the pictures -- like the shot of the cardboard President Reagan and the Little Tavern -- might not translate well. But the Chinese responded with curiosity and delight, she said.

A jury composed of representatives from Smithsonian magazine, the Corcoran Gallery of Art, National Geographic, the National Portrait Gallery, George Washington University and The Washington Post selected the photographs. The public was invited to submit photos, and there were entries from photographers living as far away as West Virginia and New York.

Washington and Peking have been sister cities since May 1984, when Mayor Marion Barry and Peking Mayor Chen Xitong signed an intercity friendship agreement encouraging cultural, educational and scientific exchanges. Last December an exhibition of photographs from and about Peking was held at the Washington Convention Center. After the Washington exhibit closes tomorrow, the photos will come home and be remounted for display at several sites here. Treasure House Reservations

The National Gallery of Art is offering a limited number of reservations for free passes to "The Treasure Houses of Britain" exhibit, which opens Nov. 3. Although the free passes will be available daily at the door on a first-come, first-served basis, reservations are recommended for out-of-town visitors who may not have time to wait in line. The gallery will restrict the number of people at the exhibition at one time, allowing visitors to enter at half-hour intervals. For reservations, write at least two weeks in advance to Treasure House Reservations, Education Department, National Gallery of Art, Washington, D.C. 20565. Include two choices of dates and times, the number of passes desired and a self-addressed stamped envelope so that the gallery can send confirmation. The passes can be picked up at the gallery's special exhibition desk on the ground floor the day of the visit. For further information, call 842-6690. Other Events

An exhibition of French cinema posters by graphic artist Jean A. Mercier opens today at Woodward and Lothrop's Seventh Floor Gallery in the downtown store at 11th and F streets NW. Mercier, 86, worked as a set and publicity poster designer in the '20s and '30s. He designed posters for films starring Charles Boyer, Maurice Chevalier and Marlene Dietrich and worked with directors Jean Renoir and Jean Epstein. Organized by the Smithsonian Institution Traveling Exhibition Service (SITES), the exhibit is the first retrospective of Mercier's work outside his native France. It also is SITES' first exhibit in a department store -- an attempt to reach people who do not go to museums on the Mall. Mercier will be at the exhibit Tuesday through Thursday, noon to 2 p.m. For further information, call 357-2700 . . .

The 12-story International Square building at 1850 K St. NW is home for a rather unusual timepiece. Resembling a large, bright star, "Timepiece" weighs two tons and measures 51 by 51 by 51 feet. It hangs in the building's atrium, spanning five stories. Washington sculptor John Safer designed "Timepiece," which in addition to keeping accurate time is an electronic sundial for 12 cities around the world . . .

Russian e'migre' Rita Tupitsin will discuss the phenomenon of "Apt Art in the '80s" -- the exhibition of art in private apartments in the Soviet Union -- at 8 p.m. Friday at the Washington Project for the Arts. The lecture is in conjunction with an exhibition of paintings and sculpture of contemporary Soviet artists at the WPA, 400 Seventh St. NW. For more information, call 347-4813.