Sarah Caldwell, new music director of Wolf Trap, flew into Washington yesterday for a day of union discussions over the use of her own opera orchestra when she brings her Opera Company of Boston to Wolf Trap June 12-15.

The problem was still unresolved when she flew back to Boston yesterday evening after talks with Sam Jack Kaufman, president of the D.C. Federation of Musicians.

Until a complaint was registered by Elliot Siegel, the contractor who handles musician's engagement at Wolf Trap, Caldwell and the Wolf Trap management had taken for granted that she would be using her Orchestra with her company's productions. She uses it on other tours and, in fact, performed with it two years ago at the Kennedy Center children's festival. In previous years, the Metropolitan Opera has used its own orchestra at Wolf Trap and the New York City Opera will do so when it appears later this season.

According to Kaufman, the Opera Company of Boston is different. "The other orchestras are under an annual contract and in those contracts are provisions for touring.This orchestra from Boston does not qualify under those terms. It's a quasi-freelance orchestra. The rule prohibits free traveling between cities where local employment is being taken away."

Kaufman was referring to Article 18 of the union's national constitution, which also states that "This law shall not be consisted so as to conflict with the engagement of traveling orchestras which accompany opera companies."

"It's unfortunate that this did not come to our attention until recently," said Caldwell. "If we had known five months ago we could have arranged schedules. I desperately hope that there will be further consideration of our problems.It may come to the point that we may have to cancel."

In yesterday's discussions between Caldwell and Kaufman, the union altered its original position and offered to allow Caldwell to bring 15 first-chair players from her orchestra, which includes retired Boston Symphony players such as Richard Burgin, former BSO concertmaster.

"That's a concession on the part of the union, but it doesn't do anything to settle the problem," said Craig Hankenson, Wolf Trap's executive director. "The problem is a matter of time. . . When you go into rehearsals with 60 to 70 players, it doesn't mean you can cut back rehearsals one-seventh. There will have to be as many rehearsals as with a whole orchestra."

The next step, according to Kaufman, lies with Caldwell. "She is now considering the terms of the offer," he said. "The timetable is hers, not ours." Caldwell could not be reached late yesterday for comment.

"It's a matter of establishing unity of style," said Caldwell, who estimated that 20 hours might be necessary for each of the operas her company will bring to Wolf Trap. "This is an ensemble. If one removes a portion of this ensemble, it is no longer the same unit."

"We have a close relationship with the local musician's union," said Hankenson. "It has been very supporting of Wolf Trap and Wolf Trap supplies a lot of employment for union members. I'm confident this can be worked out."