"Girl Friends," opening today at the Outer Circle 1. suffers from such a threadbare screenplay and tentative personality that one can't help marveling at its shlumpy appeal. A person built and clad this wretchedly would appear to be sinking fast.

Although the film aspires to contrast the characters and career choices of two young women, Susan and Weinblatt and Anne Munroe, first observed as roommates in an apartment on New York's Upper West Side, the script barely establishes the girls as nodding acquaintances, let alone friends destined to diverge along exemplary, if conflicting paths.

When Anne, a pale, pretentious WASP, announces that she's moving out to get married you feel like hollering, "Whoa!" If Anne is supposed to be more than a fleeting character, she's leaving prematurely. The sustained obligatory scenes depicting the kind of life the girls share and the kind of friendship that developes between them are missing and their absence leaves a gaping hole in the edifice of "Girl Friends" right where the front door should be.

Some screenwriters possess enough flair or experience to suggest a great deal through an artful minimum of exposition hand chracterization. Vicki Polon doesn't have that rare kind of finesse, and the director, Claudia Weill, doesn't demonstrate enough dash of improvisatory resourcefulness to conceal Polon's patchy dramaturgy.

Although biased on behalf of Susan, a Jewish girl who remains single and struggles to begin a career as a photographer, the filmmakers try to sustain the pretense that Anne is an integral part of the conception and that her aspirations and her marriage deserve respect, too. The general idea is a "Turning Point" about girls who haven't lived much or done anything particularly interesting.

Susan and Anne's sketchy association, however, won't support a dramatic relationship or verify the sentimental suggestion that feminine friendship is by definition an inscrutable thing of beauty and joy forever. Some enthusiasts have cheered "Girl Friends" as a rebuke to Paul Mazursky's "An Unmarried Woman," resented in part because its hero-married Woman," resented in part because its heroine was an attractive, secure, content East Side WASP. But if "Girl Friends" is supposed to represent the single girl's or plain girl's or Jewish girl's revenge on unfair, unworthy Gentile competition, it's a coy fraud.

The only thing preventing Susan Weinblatt from appearing more desirable than off-putting Anne Munroe is the filmmakers' determination to disguise Susan as a shambling, timid frump, a Jewish caterpillar who needs only a little encouragement and self-confidence to emerge from her frizzy. insecure cocoon. As Susan, Melanie Mayron embodies the most outrageous put on of its kind since Lynn Redgrave pretended to be a poor cow in "Georgy Girl."

The girls are even matched off in ways that ultimately confer superiority on Susan. After Anne's departure Susan must deflect a lesbian pass from a new roomie picked up on the rebound (Amy Wright contributes the film's most striking female performance as this sly, vagrant little hanger-on) and slog through an unlikely infatuation with her employer, a married, middle-aged rabbi, played with shy sweetness by Eli Wallach. With these diversions out of the way Susan links up with a suitable beau, played in amusing diffident key by Christopher Guest, who seems preferable in every respect to Anne's fussy, submissive spouse.

"Girl Friends" may seem like the Second Coming of Sheila Levine, but it appears to be heading for relative success in the Neediest Case tradition of "David and Lisa." Every so often reviewers and audiences seem to take a drably sincere little picture to their hearts: The phenomenon seems to satisfy some deep, recurrent maternal instinct.

But it's difficult to think of "Girl Friends" as a professional film without allowing a 50-handicap and a gimme every other scene. If special dispensations are also allowed for a first feature, a first feature by a promising young woman director, and a first feature by a promising young woman director groping with the subject of contemporary young women, one may begin to suspect that the fix is in.

The most one could say with confidence is that Weill might develop into a capable plainspoken filmmaker.

At the same time, however, Weill deserves a considerable amount of credit for preservering with this project from its even more humble beginnings in 1975, as a 10-minute short funded by the American Film Institute. I suspect she would develop faster if liberated from material that relied so coyly on neofeminist sentimentality.

For example, she seems much more at ease directing the actors in her cast. The men have a variety and authenticity the women lack, perhaps because Weill feels free to take them or leave them without making a big deal about it.