The ideal site for the East Coast premiere of Miguel Pinero's "A Midnight Moon at the Greasy Spoon" would be one of those little playhouses near the Broadway theater district but not a part of it. The hall would be near a corner diner like Joe's where the action of Pinero's play is set.

Pinero has brought his play to Washington, however, not New York, and Back Alley Theatre on Kennedy Street, where it will run through March 2, suits it just fine. Greasy spoons and back alleys alleys have a lot of common, and Jane Osmann has constructed a dilly of a greasy-spoon diner in Back Alley's basement home.

The walls are discreetly smeared with grime, and so is the food prepared on stage during the play. Pinero's play depends heavily on the authenticity of the atmosphere, and director Kim Peter Kovac and designer Osmann appear to have spent many happy moments eating burgers and malteds in such joints.

The old men who run the place, played by R. A. Honeygosky and Ted Rose, have been abandoned by their families, but they've got each other. They make quite a team. A menagerie of street folk pops in and out - an illegal alien Joe employs, a cop, an aging actress, a pimp. Occasionally a stranger intrudes.

As a slice of life, the first act offers some good ground meat. But the fat and the grease get a little drippy in the second act. Pinero doesn't develop his narrative; he just lets life go on. One of the most promising characters vanishes midway, never to return, the pimp delivers an aria we doubt we would have heard in such a situation, and life suddenly stops for one of the major characters for no reason except to bring down the curtain with a bang.

There are some fascinating faces in Kovac's cast, and most of their speech sounds right, too. But the most effective scene - in which a young punk dances his way through dinner - is almost speechless, Pinero should take note.