No one better knows the ups and downs of American's ballet roller coaster, and how better to survive the bumps, than Robert Joffrey.

In 1956 he founded a small, truck-and-bus touring dance unit that went on to evolve into the nation's third-largest classical ballet troupe, projectinag from the start an image of youthful exuberance. A decade after its establishment, however, the company seemed on the verge of extinction, and was saved only by the intervention of New York's City Center. This year, the troupe is re-forming itself once again, having averted fiscal disaster only by suspending operation for a six-month period, and securing an emergency grant from the National Endowment for the Arts.

The Joffrey Ballet's economic troubles are nothing out of the ordinary in the chronically precarious world of dance, but no doubt pressures have been exaggerated by the troupe's itinerant history.

"From the beginning we've been very heavily into touring," Joffrey said from New York yesterday. "And these days, no company can make money on a tour -- it inevitably ends up as a loss. Costs have been increasingly so astronomically, there's no way box-office can keep up without raising ticket prices to self-defeating levels. Last year, for example, transportation costs alone were up over 40 percent."

Joffrey, 50, seems fairly philosophical about this latest bout of brinkmanship. "It was very tough on the dancers," he said. "More so for our company than others, because we've been on the move so steadily for so long -- it broke the momentum we had built up. I hope it never happens again. There was a silver lining to the cloud, though. It did give us a chance to think and to plan, a chance our past nonstop existence scarcely ever gave us."

The "born-again" Joffrey Ballet, on the last lap of a three-month cross-country tour, tonight begins a series of five performances at Wolf Trap, where the company has appeared annually for the last decade. The programming reflects the troupe's rejuvenated spirit. Nearly half the 13 ballets will be Wolf Trap premieres, among them the first local performance of "Momentum" by Washington's own Choo San Goh; the important revival of Sir Frederick Ashton's "Illuminations," created in 1950 for the New York City Ballet; and Joffrey's own "Postcards," the first new ballet he's had time to create since the 1973 "Remembrances."

Goh's "Momentum," set to Serge Prokofiev's Piano Concerto No. 1, was originally mounted last year on the troupe's junior unit, Joffrey II. "It's a very interesting ballet," Joffrey says. "It really proved itself with the Joffrey II, which is why we've taken it into the main company repertoire." The performances here will also highlight some of the many new faces among the dancers, including Madelyn Berdes and James Canfield, formerly of the Washington Ballet. Some familiar Joffrey regulars, like Gary Chryst, Christian Holder and Jan Hanniford, have left the company since the recent layoff, but there are 10 new dancers this year, and for the first time, eight of them, including Berdes and Canfield, are stepping up from Joffrey II.

"This is a very strong advantage for us, and I'm really happy about it," Joffrey says. "Because these dancers have come from Joffrey II, we know their particular talents and needs intimately, and they know the company's character and its repertory -- their heads are in a good place."

In addition to bringing along new dancers, Joffrey hopes to put strong future emphasis on the development of new, young choregraphers, a desire he'll have a special chance to implement as a new member of the National Council on the Arts. "With the vast growth in The nation's ballet over the last decade," he says, "We've revived just about all the old classics. It's time now to try to put companies into a position that allows them to take the large risk of mounting new ballets, and that goes not only for our troupe but for ballet companies in general."

Among other new projects on the Joffrey Ballet horizon are a planned TV special to record the troupe's Diaghiley tribute, and a month's invitational tour of mainland China. "To make the China trip happen, we'll need about $400,000," Joffrey says, "so we've got a lot of fundraising ahead of us."