More than a dozen major financial supporters of the McLean Orchestra have threatened to withdraw their funding as a result of a dispute between the ensemble's board of directors and its musicians that left the group's orchestra pit nearly empty.

The majority of the volunteer orchestra's musicians along with the music director and conductor, Dingwall Fleary, abruptly left the orchestra in May after the board decided to replace Fleary at the start of the 1987-88 season. Fifty-one of the orchestra's 55 members regrouped under the name McLean Symphony and hired Fleary as their conductor.

Now some patrons who have regularly donated thousands of dollars to the McLean Orchestra since its start in 1972 have decided to bring their loyalty, as well as their checkbooks, to the newly formed symphony.

"I have had calls from past orchestra board members who were always staunch contributors . . . and they said that whatever they have seen or heard has not swayed them," Fleary said. "We are the organization they will continue to support."

Fleary said he resigned his $19,000-a-year part-time position as music director and conductor of the orchestra because of a contract the board drew up that prohibited him from serving in a similar job for "any other orchestra, symphony or similar music organization in the metropolitan Washington, D.C., area." As a free-lance musician, Fleary said, "that was something I could not accept."

One McLean Orchestra board member, who asked not to be identified, said the board had been considering Fleary's dismissal as orchestra leader "for several years. This was not something that occurred one evening at a board meeting."

The member said the board had concerns about Fleary's ability to manage the growing orchestra and its annual budget of almost $60,000. A report of the orchestra evaluation committee dated April 1986 recommended that the board either "retain the present Music Director as our sole musical leader and conductor and limit his administrative and management responsibilities," or "move to a restricted role for Fleary and the introduction of new conductor options to the orchestra and the community" or "move immediately to replace Fleary and organize for a season of guest conductors . . . . "

Ultimately, a majority of the then 17-member board voted to offer Fleary a new contract that did not go beyond the 1986-87 season, which begins in October.

Stanley Richards, who serves on the McLean Orchestra's board of directors, acknowledged that fund-raising efforts would be more difficult for his group this year.

"There is a serious problem whether the community will financially support two organizations," Richards said. "I'm sure there are some individuals who contributed to us in the past that may not contribute to us in the future."

James R. Price, a member of the board of directors of the newly formed McLean Symphony, said his group has already filed with the Internal Revenue Service for tax-exempt status, which will enable donors to deduct financial contributions from their annual income tax. The symphony cannot begin active fund-raising efforts until it receives the exemption from the IRS.

In the meantime, symphony members said they have organized a massive letter-writing campaign notifying McLean residents and others of the new group's fall schedule. Symphony musicians also said they have received calls from many of the McLean Orchestra's longtime patrons who said they intend to switch their financial support to the symphony this year.

One couple, who has donated $250 a year to the orchestra for at least six years and asked not to be identified, said this season's check will "definitely go the McLean Symphony. Those folks are the ones who are really what it's all about."

Dr. Barry Byer, who said he has donated at least $100 a year to the McLean Orchestra since it started in 1971, said this year he will write his check to the McLean Symphony.

"I've talked to other people who have been supporters and they seem to feel as I do . . . . The lack of tax-exempt status doesn't bother me," Byer said of the new symphony. "What I've been supporting all along is not the board of directors -- it's the group that makes the orchestra."

Jane Kornblut, president of the 15-member McLean Orchestra board, said three-fourths of the ensemble's funding comes from cash contributions by individuals, corporations and local businesses. She said fund-raising "is going to be very difficult . . . this is a very competitive area. We certainly rely on the support of the community for our funding."

Another major contributor to the orchestra, who also declined to be identified, said he is uncertain whether he will remain loyal to the McLean Orchestra. "I'm waiting to see what Dingwall's group is going to do," he said.

Local business owners who previously have placed advertisements in the orchestra's program guide said they might pull their ads from the orchestra and give their money to the symphony instead.

The McLean Orchestra recently has hired Col. Arnald D. Gabriel, chairman of George Mason University's performing arts department, to serve as its new conductor and music director. And last week, the orchestra started to hold auditions in an effort to fill the large gap left by the departure of its former musicians.

"We have about half of what we're shooting for," Gabriel said.