Peter Allen catapults himself out onto the stage, in a white sports coat and a pink carnation and a Hawaiian print skirt bright enough to bring an adrenaline rush to even the most 'Luded-out undergraduate eyeball, and he springs a hip, stands arms akimbo, smiles a manic, ingratiating, how-do-ya-like-them-maracas grin, attacks the piano (which is adorned with fresh pineapples), shimmies his shoulders and begins to play this irresistible Chiquita Banana tikki-tikki-tikki.

"Champagne?" The sweet young thing next to you at the concert offers a belt of brown-bagged Asti Spumante and assures you don't get uptight about Things (it's not that, Pablum Breath. It's just that one doesn't remember growing to be 1,000 years old), while a couple of seats over a gentleman of the gay persuasion mutters, "I'm so vulnerable to P.A. now, he's gonna come on and make me go bazooey. Sing 'Rio!'"

"I Go to Rio" is Peter Allen's greatest hit (No. 1 in France and Australia at any rate) and after 18 years in show business - highflying in the '60s as Judy Garland's opening act and Liza Minnelli's husband - Peter Allen, it is said, is about to become an overnight sensation.

Allen, who was in town last weekend to play American University (he returns next week to the Warner), makes it on an appeal that has been called "pansexual" by no less a dancing fool and society observer than Dan Rather. Allen's new manager, the formidable Dee Anthony, prefers to explain it by saying that "Women love him. They find him very sexually attractive," which is more or less true (he has these great loose-jointed legs and navy-blue-and-white-spectator shoes). But Allen has a big-city gay cult following, and maintains that the larger audience to which he aspires rejects tired old macho totems (a trend even Mick Jagger, self-appointed king of the gender blur, might keep a weather eye on. It was rock and roll's machismo, after all, in whose tradition Jagger sang all those sweet little songs about having so-called "girls" under his so-called thumb).

Allen camps it up on stage as much as Jagger does, swings a mean pelvis, a hot microphone, treats his piano bench like a pair of parallel bars at Fred Astaire's dancing school, but he threatens no one - except maybe with a champagne-stoked urge to rumba.

"There's no real role for men on the stage now," says Allen. "The Dean martin, Frank Sinatra mold doesn't really work at this point. I touch areas only a girl would do - women can get away with more on stage. Can you really see John Davidson bursting into tears? Besides," he says, "we're not a handsome man, we don't have your clasic features and wavy hair. There's a lot of people who are uncomfortable with the male role. I'm carrying on a weird show business tradition of different sexes or no sex," says Allen, and mentions venerable British and Australian female impersonators like Danny LaRue and Barry Humphries. "The main thing I want people to know," says Allen, "is that we're not watching television here. It's LIVE."

Television is a great scapegoat of Allen's and his outrageousness is pretty much calculated to pique the record-buying impulse of the television-bred, down-popping generation. "Instead of audiences smoking dope and taking downs and passing out in the seats," says Allen, "some form of entertainment is coming back. There's not much entertainment around for people who grew up in the '60s and who are now 30 and who want some fun."

And the whole pro-outrage syndrome is related to a concept of performing Allen learned - perhaps from Elton John's enormous success at it - but definitely from Judy Garland. "Everything lay in reality with her," says Allen. "That's the one thing I learned from her. She made everything she sang real, and even when it was bad it was better than most peoples' being good. I think that's why she failed on television. She was too emotional. You don't want to stand up and clap and burst into tears in your living room on Sunday night."

Allen's performance is a combination of the saloon singer's self-mocking patter, free-asociated requests shouted by the crowd, a kinetic ricochet between cavorting on the piano bench and wonderful swivel-hipped dancing on the stage in which he sheds first the coat, then the shirt, to reveal a low-cut red-sequinned corselet and the aforementioned ever-rhythmic maracas. Hotcha.

So, under Anthony's management, Allen has stopped writing and performing the bathetic, quiveringly vulnerable songs of his first four albums - songs that picked up a gay following as much as Garland herself did. He is opting now for fizzier Latin rhythms, and no doubt, ballads along the lines of "I Honestly Love You," which he wrote and which won three Grammies for Olivia Newton-John.

Allen's new album has sold 52,000 copies, more than all the others combined, but still no hit by American standards. He is now on a demographically calibrated tour of campuses and clubbier, small 3,000-seat halls, to push the new live performance album, "It Is Time for Peter Allen." These are favored techniques of De Anthony, who started out managing Tony Bennett.

Last year, by means of three years' blitzkrieg tours, Anthony calibrated Peter Frampton into the year's most popular male recording artist. Frampton's lives album sold 14 million copies. The idea, says Anthony, is that people buy the album as a souvenir of an enchanting live performance, thus hyping sales, getting hit singles, radio air-play time, gold, platinum, millions of dollars, name in lights (Frampton has just done a movie), etcetera, etcetera, etcetera.

Anthony "discovered" Peter Allen a year ago, when Allen was selling out The Bottom Line, Allen's usual sort of small intimate New York club. Since the breakup of the Minnelli marriage in 1970, Allen had been pegged to an increasingly popular, but - well, esoteric - club scene in New York. He began at Greenwich Village's Bitter End, followed Bette Midler at the Continental Baths, moved on to Reno Sweeney.

"The day I saw him at The Bottom Line," says Anthony, "A & M Records had just dropped his contract." Anthony brought his family to each night's performance, literally went back stage at the end of the engagement, invited Allen home for pasta ("Everything is done over pasta," says Allen), said there was nothing underground about him, "You deserve to be a star."

"Society is ready for him," Anthony says. "Kids want to be entertained today." So Anthony sent Allen home to Australia this summer, where he drew 10,000 for one show and made "I Go to Rio" a hit. "That's where we blew it wide open," says Anthony. "Open a crack in that door and I'll put my body right into it. It will be a hit in America. It's got to be. I don't know what the hell is holding it back . . ."

Meanwhile, Peter Allen thinks back on the Minnelli days, jet lag days he fell asleep in discotheques, in front of the Beatles, Fonteyn and Nureyev, at Noel Coward's house, at George Sanders' house in the middle of Judy Garland's singing a duet with Vivien Leigh. He knows a little something about celebrity. "The marriage broke up," he says, "for all the obvious reasons. Two people in show business. The thing they write movies about. Girl becomes big star. Husband stays home. Liza staying home to cook little meals for her husband (She's a very good cook, but she only had about four things she could do). And there was no women's movement then, and I didn't say, 'Stop trying to work the washing machine and get out there and dance.' We were trapped in this young, happy New York marrieds thing and the only way to get out of that is to become Scott and Zelda, which is fun when you're 20 and exhausting when you're 25 . . ."

Now, at 33, Allen is up, if not out. He teases audiences about being gay. To one, he said, "I know you must be asking yourself by this time, 'Is he or isn't he?' Well, yes I am . . . Australian" He sings, in a pliant tenor, a delicate ballad about "Two friends Carole Bayer Sager and Marvin Hamlisch. He follows "Two Boys" up with a wry, "We don't know what it's about, but we like it."

As for the stardom Dee Anthony plans for him - well, Peter Allen is a pro. "I get pushed out in my sequins and Hawaiian shirts," he says quietly, "and hope they stand up at the end."

They do. In the middle of exam week at American University, he drew 600 people less than capacity, to two shows. The audience gave him standing ovations. Hotcha.