Why is so much of Boston's top art talent leaving town?

It's been a turbulent time in the Boston arts world: In a brief few weeks the heads of four major institutions have resigned.

* Conductor John Williams announced his resignation June 13 from the Boston Pops after his new song was hissed by several musicians during a rehearsal. (At presstime the trustees were negotiating for his return.)

* Artistic director Peter Sellars announced June 7 he was leaving Boston Shakespeare Company to take a position with the Kennedy Center for the Performing Arts in Washington.

* Violette Verdy quit her post as artistic director of the Boston Ballet last weekend. Her resignation follows Joel Garrick's, who stepped down as president last week.

* Kenworth Moffett, curator of 20th-century art at the Museum of Fine Arts, is leaving for a writing career.

On the surface, perhaps, these four have little in common. But, aside from Mr. Moffett's case, problems with the boards of directors or managements - either because of meddling or a lack of support - are a common under-lying factor, say observers close to the scene.

''Board members sometimes leave their business sense and acumen outside the board room,'' says Maryellen Cabot, a member of the Massachusetts Council on the Arts and Humanities. ''They don't understand that artistic people are just as professional as business people - and need the lines of command to be as distinctly drawn.''

It's a time of transition for these institutions, many say, and the choices made by those in charge could result in stable and vigorous companies - or a continuing exodus of artists.

The management of the Boston Pops is perilously close to losing its popular Oscar-winning conductor, John Williams. Pops members have speculated that the hissing incident was the ''straw that broke the camel's back'' - that Mr. Williams's deeper dissatisfaction lay with management's lack of control over unruly members, and his lack of artistic control over hiring and firing.

Various members said they were surprised Williams took the hissing ''so seriously.'' Reports are legion of Pops players hissing at new music or new arrangements, looking at watches, reading, or talking while colleagues played. Associate conductor Harry Ellis Dickson says he, too, has had to contend with decorum problems. Arthur Fiedler, Pops conductor for 51 years, had to put up with constant friction, Mr. Dickson adds.

''There were knock-down, drag-out fights with him,'' Dickson says at the office of Boston Symphony Orchestra, the Pops's parent organization. ''But Fiedler loved it. John was a bit more sensitive.''

Williams, who will finish out the Pops season July 8, was considered the ideal choice for the job. He has an extensive classical background. As a highly acclaimed composer of movie scores (''Jaws,'' ''Star Wars,'' and ''Indiana Jones and the Temple of Doom'' among them) and of the official theme song for the Los Angeles Olympics, his name was big among both adults and youth.

Tuesday night's meeting between Williams and the trustees signals a possibility that the conductor will pick up his baton in Boston again. ''It was an informational, positive session,'' says Caroline Smedvig, director of promotion who attended the meeting.

If Williams does return, will that mean a overall change in policy? Have the musicians been permanently shamed into better behavior?

''If anyone tries it again, they'll be immediately squelched by the other players. We're too embarrassed to ever let it happen again,'' says one Pops musician.

Other sources scoff, saying the problem is endemic not only to this orchestra but also to other major ones. After the embarrassment dies down, it will be ''business as usual,'' says one observer.

The loss of Peter Sellars and Violette Verdy is ''a real blow,'' says Anne Hawley, executive director of the Massachusetts Council on the Arts and Humanities.

The loss to Boston Shakespeare of Peter Sellars is enormous. A fledgling company whose productions were often mediocre, it was shot into the limelight when it nabbed this controversial and prolific young director last fall. Its production of ''Mother Courage and Her Children,'' starring Oscar-winner Linda Hunt, was highly regarded nationally, and ''The Lighthouse'' received international attention.

Now the Boston Shakespeare Company has to figure out how to sustain this national momentum, says Jack Thomas, director of marketing. ''With all this attention, we have the obligation to attract the audience's eye and the press.''

Mr. Sellars has stated that lack of funding was one problem. Next year's budget is estimated at close to this year's $840,000 level; Sellars sought $1.2 million. The Kennedy Center's greater financial resources are one draw. But also appealing is the greater artistic control he will have; as director of the newly created American National Theatre Company, Sellars will be in charge of development, production, and presentation of a wide range of plays in three of the five theaters.

The resignation of Violette Verdy from the Boston Ballet is also serious. Since May the company has lost its founder, E. Virginia Williams (who passed on May 8); president Joel Garrick; and now artistic director Verdy. It's a company with literally no one at the helm.

The upheaval appears to be taking its toll on the dancers. In the wake of Miss Verdy's resignation, principal dancer Marie-Christine Mouis and corps member Alexandre Prioa have announced they are leaving the ballet, as have resident choreographer Ron Cunningham and ballet mistress Carinne Binda. Other company members say they are awaiting the announcement of Miss Verdy's replacement before deciding what to do.

The company was a fairly stable family-like organization under Miss Williams, but in recent months it has seen turbulent wrestlings for control between Verdy and Garrick.

Under Garrick's 18-month administration, contributed income and subscribers doubled. But artistic friction undermined the improving financial picture. ''Joel was never able to build a collaborative relationship with Violette and didn't build a team administration,'' says John Humphrey, chairman of the ballet.

At the same time, Miss Verdy was also fighting members of the board. Several people close to the ballet said these members invaded her artistic domain and did not give her support for her goals, or for the staff she needed.

It is friction at the top that may prevent companies like the Boston Ballet and Boston Shakespeare Company from becoming strong and vibrant. Until the lines of command are clearly established, artistic initiative and integrity is sapped, dancers wait for the other toe shoe to fall, investors chew their nails, and Boston audiences are the true losers.

''Miss Verdy and Mr. Sellars brought enormous genius to their companies, but we have to pick up the pieces,'' says Ms. Hawley. ''It is of the utmost priority for the boards to grow a large artistic vision and to recruit two world-class talents to move the organizations forward,'' she says.

The departure of Kenworth Moffett from the Museum of Fine Arts is a simpler one - and one that can have positive impact on both Mr. Moffett and the MFA. He gets the life of a writer; the museum gets a fresh perspective to expand its selection of contemporary art.

The museum didn't have a department of contemporary art until Moffett started it in 1971. During his 13 years at the MFA, he mounted major retrospectives of Jules Olitsky, Anthony Caro, and Fairfield Porter, and acquired more than 100 works of modern and contemporary art.

''Starting from zero, Ken made a concentrated effort to create a distinctive collection with an emphasis on abstract and realist painting,'' says MFA director Jan Fontein.

But Moffett has been criticized for favoring color field abstractionism over other contemporary styles.

For 13 years Moffett, with his specific point of view, ''created the rules for the ball game played at the MFA,'' says Bernie Pucker, owner for 17 years of Pucker/Safrai Gallery. ''It's a major institution that has had very little interest in 80 percent of what was going on in the city.''

Moffett's departure gives the MFA the opportunity to become more eclectic in its selections of contemporary art, say arts observers. Although it's too soon to track any new direction, Fontein says, ''With a new person you get a shift in focus; we'll probably get a wider interest in other aspects of contemporary art.''

Pucker says, ''You get someone in there that has the ability to network, has astute political goals, and commitment to artists; then you get people saying, 'Boston? It's one of the best contemporary-arts communities.' ''