The studio audience at last night's Mama Cass Elliot television special on the American Broadcasting Company appeared to be made up largely of her devoted fans. It's probably just as well. Mama Cass needed all the help she could get, because the producers afforded her very little.

To apportion blame for last night's taped fiasco would require a lengthy credit list. Suffice it to say that the direction was execrable, the writing witless and the production torpid. Indeed, for a program obviously aimed at a younger audience, the performers appeared to be suffering from tired blood.

Buddy Hackett tried hard but sank under a leaden script, and Martin Landau and Barbara Bain, the former co-stars of "Mission: Impossible," were unbelievably inept in an idiotic skit about computer matchmaking and added no luster to their names as vocalists.

Joni Mitchell, a folksinger with a winningly plaintive little voice, would be much more effective if she invested in a few lessons in voice projection and elocution, and Mary Traverse and John Sebastian are more interesting to look at than to listen to.

As for Mama herself, she has a pleasant enough voice, but it lacks in color and in sophistication. She comes over best in dreamy ballads and rock songs like "California Dreaming" and "Dancing in the Streets." Her limitations become pronounced in a standard like "I Can Dream, Can't I," which demands more intelligent phrasing than she is now equipped for. And, while she makes an intelligent and likable hostess, she is not forceful enough for the take-charge role. In short, she will require more seasoning before she is ready for her own show.