NEW YORK -- First of all, there's going to be an orchestra. For all its 30 years here at the tiny Sullivan Street Playhouse, "The Fantasticks" has been performed with just a piano and a harp, but on the 30th Anniversary Tour -- it kicks off at Wolf Trap today -- 17 musicians will sweeten familiar tunes like "Try to Remember" and "Soon It's Gonna Rain."

And there'll be a chorus. For the first time, creators Tom Jones and Harvey Schmidt are adding seven ensemble singers who also dance. There's no room to dance at Sullivan Street, where if The Boy and The Girl aren't careful, they're likely to kiss the guy in the front row instead of one another. But the road show boasts an actual choreographer and two production numbers.

And a star -- the perennially dashing and mustachioed Robert Goulet -- as The Narrator. And new sets and costumes. And a big sword fight. And a new song called "Abductions," which replaces the humorous ditty that celebrates rape, a subject about which theatergoers may have lost their sense of whimsy since the world's longest-running musical opened in May 1960.

"This is a 'Fantasticks' that's never been seen or heard before, a totally new creation," says Jones, the playwright and lyricist.

"It was a fine line to walk," puts in Schmidt, the composer, Jones's friend since they were undergraduates at the University of Texas and his collaborator since 1950. "We really didn't want to violate the feelings of the show." Mucking about with "The Fantasticks" is something like burning the flag or, perhaps more aptly, burning an annuity.

It's been playing here in this brownstone in Greenwich Village ("the Mother Ship," Schmidt calls it) forever, hasn't it? The upstairs lounge, where Jones and Schmidt sit talking about the tour, has become a kind of museum, hung with foreign playbills and original costume sketches and photos of the stars (Jerry Orbach, F. Murray Abraham, the pre-diplomatic John Gavin, plus Bert Lahr and Ricardo Montalban in the '64 televised version) who've rotated through the production. The room is not vast but the memorabilia keeps multiplying ("The Fantasticks" has had more than 11,000 amateur and professional productions in 69 countries), so Jones and Schmidt have been unable to hang anything new in, oh, about 15 years.

The theater's size -- just 153 seats -- has helped keep the show running all these years, the overhead being low enough that sold-out weekends compensate for those weekdays when, Jones says, "the cast may outnumber the audience." The show's closing was announced in 1986, a prospect greeted by protests and a wave of ticket-buying that's kept the box office open ever since.

Yet Jones and Schmidt have mused for several years about expanding the romantic little confection, with its deliberately bare set and such rudimentary props as a painted wooden moon hung on a nail, into a bigger, fuller musical.

The conventional wisdom has been that "The Fantasticks," which attracts adjectives like fragile, resists such amplification. In fact, the Shuberts wanted to take the show to Broadway quite early in its run, an offer Jones and Schmidt declined. "We were convinced -- as many people are today -- that it really wouldn't work in a larger setting," says Jones.

Or would it? Two years ago, the team was invited to China to see the Peking Opera performance of "The Fantasticks" in a 6,000-seat theater. "There are no small theaters in China, you may quote me on that," says Jones, at 62 the senior partner with the whiter goatee. "It seemed to play very well."

They directed a Japanese tour that played 800- to 1,000-seat theaters. They heard the Boston Pops play a medley of the show's songs, which by now deserve to be known as standards. "The music seemed to take very well to the full, big sound," says Schmidt, who's about to turn 61 and wears the grayer goatee. They began to take notes.

Hence, the 30th-anniversary tour, as good an excuse as any to book "The Fantasticks" into 40 cities: Philadelphia; Grand Rapids, Mich.; St. Louis; Memphis; Houston.

It had a shaky start -- a Minneapolis tryout was canceled, the theater management blaming poor ticket sales, the creators (and, for this tour, directors) pointing out that the theater shut down altogether shortly thereafter and blaming its management. The tryout was held in Des Moines instead, followed by a preview at the Music Hall in Dallas, where the critics were kind and the ticket sales were soft at first, but built. Wolf Trap, which wants to sell 5,000 to 6,000 tickets each night of the run, is next.

Jones admits to some nervousness. "Sending out a massive tour, in which the producers have invested a million dollars, of our humble little show," he frets.

"Which cost $15,000 here," Schmidt adds. The show's return to its original investors, whose ranks do not include Jones (who regrets it) or Schmidt (who doesn't), has been well over 12,000 percent.

"We think it will work, but there's always the vivid possibility that we're wrong," Jones concludes.

The current tour's potential payoff to Jones and Schmidt goes beyond royalties. They're already discussing the possibility of a cast album, and a television special that could then be marketed as a videocassette. "Family entertainment, you know," Jones says. There could be a long post-tour run in Los Angeles, say, or Chicago.

All these things can help stoke the New York box office and, more significantly, increase the sales of secondary rights, the major source of earnings for the partners. There's talk, too, of a touring revival of the second biggest Jones-Schmidt hit, "I Do! I Do!" Perhaps, if their plays move back into the public eye and the tour's grosses look impressive in Variety, Jones and Schmidt may have better luck getting their newer work produced.

They've been a theatrical team longer than Kander and Ebb, almost as long as Comden and Green if you count undergraduate productions. Yet since 1963's "110 in the Shade" (based on "The Rainmaker") and 1966's "I Do! I Do!" (the first two-character Broadway musical), they haven't had a Broadway hit. "Celebration" failed to connect in 1969. A musical based on the life of Colette has appeared off-Broadway but not on-.

Their biggest disappointment has been "Grover's Corners," a musical version of Thornton Wilder's "Our Town." It was staged in Chicago in 1987 and, Jones says, "I don't think we've ever done anything better." But they couldn't raise the money for a Broadway production (no one wanted to see a musical that ended with everyone dead, producers said). The show has too big a cast to be economically feasible off-Broadway. Plans for a year's tour with Mary Martin as the Stage Manager fizzled when she became ill. The rights from Wilder's estate have since lapsed.

"It is frustrating," Jones acknowledges. "We'd just like to get {these plays} on; it doesn't have to be someplace grand. It's humbling. But not defeating."

For the partnership endures. Jones has never written with another collaborator, though he once used Jacques Offenbach's music for a project. "It helps when they're dead," Schmidt says. He's never had another partner either, unless you count the film score to "Bad Company," written with another Texan, Robert Benton. Why have they stuck it out for most of 40 years? "Time passes quickly and we work slowly," Schmidt says.

They find it difficult to formulate why "The Fantasticks" has run for 30 years. Some combination of lovely music, an allegorical fable that draws family groups speaking many languages, and a small weekly nut, apparently. And luck.

"Sometimes we're anathema to the cognoscenti; sometimes we're caviar," Jones shrugs. "It's nice to live long enough to go in and out of fashion."