Having scored a great success with "Nightmare!," the same people at the New Playwrights' Theatre have used the same formula for "Out to Lunch." It's not such a success this time around.

The pattern is a pretty good one, and may yet work again. Grandma and the boy and girl next door, representing a cheerfully dumb, nostalgic American innocence, are juxtaposed against less innocent pop figures, as played by a trio of singers who are quick at getting in and out of costumes and accents. In "Nightmare!" it was wholesome Henry and Bambi in a nightmare world of gangsters, and in "Out to Lunch" the equivalent couple is wholesome Sparky and Binky in a time-machine world of historical characters.

Both plays are written by Tim Grundmann and directed by Ken Bloom, and both have the energetic talents of Barbara Rappaport, Tanis Roach, A. David Johnson and Jan Frederick Shiffman as Grandmas and adaptable threesomes as choruses. Both have bouncy songs and a humor based on mixing the naive with the crass.

But these are just pushed too far in "Out to Lunch." Attila the Hun singing mouthwash commercials is too college humor; so is Shakespeare watching his "Romeo and Juliet" turned into a strip act. The fun in "Nightmare!" floated on a cloud of lovability - quickly ruined in "Out to Lunch" when dear venerated Grandma gets into a hair-pulling fight.

It's a shame, especially as there are several original charms in "Out to Lunch," such as the motel room. Art Deco atmosphere ingeniously suggested in Kit Grover's painted set, and the staging of a scene in which the trio, now representing pixies, race about, looking way up at people - of the same actual size - who look down at them.