A theater museum in the heart of the Broadway theater district! What could be more logical? Or theatrical? So this month -- after five years of planning and dreaming and fund raising -- the Broadway branch of the Theater Collection of the Museum of the City of New York opened its doors. It occupies 1,500 square feet of space off the Minskoff Theater arcade between West 44th and 45th Streets.
The small wonderworld of theatrical memorabilia has opened its promising career with an exhibit entitled, ''An Actor's Life,'' dedicated to the player folk who have helped make American theater in the last hundred years or so. Besides displays of photographs, paintings, caricatures, costumes, props, and other artifacts, the premiere attraction includes a light-and-sound show narrated by Gary Merrill and a charmingly forthright videotape interview with Helen Hayes.
A foreword to the catalog of ''An Actor's Life'' states that the theme was chosen ''carefully and deliberately. It tries to do the impossible by attempting to tell something of the 'other' life of a stage actor through the usually static medium of the museum interpretation. . . .
''This exhibition pays tribute to stage actors because of their contributions to it. While it is true that actors are the most visible of the theatrical collaborators and are considered the most vital part of the theatrical collaboration in the public mind, they are also first on the firing line when the slings and arrows of criticism are hurled. Because their skills are born of great personal sacrifice and their dedication eats into the very fabric of their lives, there is no adequate personal way to applaud them outside the walls of the theater. In this small but visible way, The Theater Collection congratulates New York's actors by dedicating to them this first exhibition in its new gallery in the Theater District.''
The museum premises have been ingeniously fitted into the available space by architect Martin Bloom. Stage designer David Mitchell and lighting designer Ian Calderon have added their own creative talents to dramatize the treasures assembled by curator Mary Henderson from the museum's vast collection.
A series of exhibits combine photographic essays (photos from the Joseph Byron Collection and the files of Rivka S. Katvan) and display cases. Photographic subjects range from Lillian Russell to Elizabeth Taylor and from David Warfield to Jim Dale. They transport the visitor to the on-stage and backstage world of the player.
The individual displays of wardrobes and props dip nostalgically into the theater's past: the glamorous Hattie Carnegie gown worn by Gertrude Lawrence in ''Susan and God''; Jeanette Lilford's pink ''soubrette'' costume and, beside it, her vaudeville trunk; Lillian Gish's Henriette costume for the film ''Orphans of the Storm.'' And so much more.
The light-and-sound show creates its own vivid impressions. With the recorded voice of Gary Merrill speaking Dr. Henderson's commentary, the show lights up plastic sculptures of several legendary stage figures. They include Joseph Jefferson as Rip Van Winkle, Ethel Barrymore as Mme. Trentoni, Tallulah Bankhead as the star of NBC radio's ''The Show of Shows,'' and an airborne Mary Martin in the Peter Pan costume she wore both on-stage and in the historic 1955 television broadcast. The visual and audio elements blend remarkably in this vivid look at an actor's life.
With Playbill publisher Arthur Birsh as chairman, the Friends of the Theater Collection helped raise the $290,000 necessary to launch the annex at the Minskoff. Contributions came from foundations, corporations, unions, theater-interest groups, and individuals. The museum has the space rent free for one year, after which it will pay $1,250 a month, considered a modest figure in view of the location in the heart of the theater district.
The mini-museum is open Tuesdays through Saturdays from 12 to 8 p.m. and Sundays from 1 to 5 p.m. It is closed Mondays. Admission is free, with a suggested donation of $1 for adults and 50 cents for children and older people.
By ironic coincidence, the museum opened in the same month that saw the shameful demolition of two neighboring irreplaceable theaters -- the Morosco and the Helen Hayes -- despite heroic, last-minute efforts to save them and legal appeals that went all the way to the Supreme Court. If the rescue efforts had succeeded, the actors and other theater people who had rallied to the cause would have deserved a major share of the credit. It would have been another reason for celebrating ''An Actor's Life.'' As it is, in a city where property values too often dominate humane and cultural values, Broadway's gemlike new theater museum shines like a good deed in a naughty world.