Visit the Warner Theater during the next six weeks and you are guaranteed to exit whistling - even if you've never whistled a note in your life.

The insurance policy that carries this payoff is called "Ain't Misbehavin'" and it arrived in high style last night, strutting, preening and flashing virtually every prize a Broadway musical can flash.

The visible and audible ingredients of the show are a topnotch band, five smooth performers and the hovering musical presence of Thomas "Fats" Waller, the exuberant swing and stride stylist of the '20s and '30s.

"Ain't Misbehavin'" is a revue - virtually a lost theatrical species. And it carries us back to a lost era with what certainly looks like authenticity. Adaptor and director Richard Maltby Jr. has tried to serve up Waller's music not only in its original form (with some added lyrics) but in its original surroundings, too - which means jazzera Harlem.

The effect is convincing, and engaging, thanks first of all to J. Leonard Oxley's band, with Oxley himself at the piano. Arthur Faria's choreography, too, has a formal but slippery depression look, especially as rendered by Ben Harney, who can jump high, bend low and slink from side to side, with enormous grace.

Harney may be the standout dancer of the group, but all five performers make themselves memorable.

In the middle of Act Two, Teresa Bowers and Yvette Freeman do a bosom-to-bosom, perfectly synchronized performance of a song called "Find Out What They Like" (". . . and let 'em have it just that way"), whispering one moment and hollering the next. The will knock you dead.

Another high point is Adriane Lenox's rendition of "Keepin' Out of Mischief Now," and unexpectedly urgent and poignant melody, given the lighthearted title. Lenox's superior singing voice is mostly hidden behind her gangly, frenetic dancing and mugging, but in this one song about a woman's loyalty to her absent man, she shows us she is made of stronger stuff.

The lyric to "Keepin' Out of Mischief Now" is by Andy Razaf, who seems to have been the author of many of the most affecting lyrics in the show, including the one shocker in this carefree evening, "Black and Blue," in which the whole company sings: "I'm white inside, but that don't help my case, 'cause I can't hide what is on my face."

Ken Prymus, the actor who somewhat resembles Waller but is never said to be him, is remarkable neither as a singer nor as a dancer. But simply opening his mouth wide - which he can do with or without showing a set of teeth that could throw a beaver into a jealous rage - he is terrifically funny. As is his whiskey-guzzling, dead-earnest performance of "Your Feet's Too Big," in which he warns his lady friend her toes will stick out of the casket when she is buried.

There are times, especially in the first act, when the performers are calle on to resort to some fairly shameless and only marginally comprehensible business to hold the audience's attention. If somebody made a federal case of it, much of the last 20 minutes or so before the intermission would probably be ruled immaterial, not to mention immature.

And the company cries out for one real knockout singer with, for a colossal theater's sake, a colossal voice. Despite the generally skillful amplification, these performers come across, on the whole, as sounder in the shaking an dclowning than in the singing department.

On close examination, the set may not add up to much - one extremely handsome upright piano with locomotive powers, a rim of colored lights, a bandstand that slides forward and back, a few tables and chairs. But it has a deep purple grandeur that is enhanced by the snappy period costumes and smartly complemented by the elegance of the theater.

The Warner was looking its chic and elegant best last night. It was also, however, producing a mysterious and fairly constant roar from the general vicinity of the stage that was, presumably, associated with the process of ventilation.

If the Warner management is looking for things to manage, it might begin with that formidable noise and the apparently inadequate capacity of its Ladies' Room, where a long and intimidating line formed at intermission last night.

In the meantime, happily, the theater has an attraction that makes its hardships worth enduring. CAPTION: Picture 1, Teresa Bowers, Ken Prymus, Adriane Lenox, Ben Harney and Yvette Freeman in 'Ain't Misbehavin'