FESTIVAL, a musical by Randall Martin and Stephen Downs. Directed by Wayne Brian; scenery and lighting by George Gizienski; costumes by Madeline Ann Graneto.

With Gregory Harrison, Maureen McNamara, Bill Hutton, Michael Magnusen, Lindy Nisbet, Roxann Parker, Michael Rupert, Leon Stewart and Robin Taylor.

At Ford's Theatre, 511 10th St. NW, for an open ended engagement.

Like a colossal, grinning candy apple in denim diapers, "Festival" rolled onto the stage of Ford's Theater last night, reminding us that San Francisco exports not only political fanaticism but its own unmistakable brand of naivete.

This "musical mischief," allegedly based on a medieval love story, is as innocent as Dreyfus, Sacco and Vanzetti and the Count of Mote Cristo put together. But if you are under 12 -- or have leanings in that direction -- "Festival" may be just your cup of herbal tea.

The story has something to do with young lovers, intolerant elders, pirates, tempests, amazonlike warriors and mistaken identity. But the story is never allowed to amount to more than a momentary diversion from the multifarious diversions that carry the show forward, each more unsubtle and irrelevant than the last.

"Festival" does not ask you to suspend disbelief so much as to give it a great big kiss.

And at its most likable, it charges forward with splendidly off-the-wall sight and sound gags, preposterously saccharin songs and acting that suggests that any cast member who stops smilling for even a moment knows he is going to be whipped. The two young lovers, played by Bill Hutton and Maureen McNamara, are as earnest and wholesome as the leads in a chewing gum commercial, which is exactly right. McNamara, in particular, with hair as red as the most startling autumn leaf, a honey of a voice and an absolutely total commitment to the challenge of taking dumb dialogue seriously, reminds us what a difficult, underrated business being a musical ingenue is.

the parents and asorted peripheral characters in the tale play their parts with somewhat less conviction, but then what choice do they have in a play that calls on them to do such things as pass out sheet music to the orchestra before a number and tend a pair of stuffed sheep?

As the narrator, Gregory Harrison manfully succeeds in keeping a smirking face through some leaden speeches, and makes the most of the few genuinely inspired jokes in which he is permitted to participate.

"Festival," from its opening song onward, aims to carve out a modest place for itself alongside such classics of broad, self-mocking musical comedy as "Once Upon a Mattress" and "A Funny Thing Happened on the Way to the Forum."

In fact, its opening number, called "Our Song," has grabbed just about everything grabbable from "Forum's" "Comedy Tonight," except, of course, Stephen Sondheim's wit. And as the show continues, it reminds us what a remarkable feat those other musicals pulled off, parlaying similarly inane story elements into entertainments with charms -- sometimes separate and sometimes common -- for adults and children alike.

The music to this affair is so bouncy that the musicians actually bounce up and down in the orchestra pit, but the songs have nothing, in general, to do with the story -- another unfortunate point of comparison with "A Funny Thing..." whose score admirably resisted the temptation to go for "hits" in favor of serving the story in both mood and substance.

But enough of comparisons. On its own distinctively low plane, this is a show with a certain rambunctious appeal.