Mozart in a coffee shop: provocative, thoughtful, too far from the original?

Castle Hill is the focal point of the sprawling Crane Estate on the historic shores north of Boston. In the summer the manor house becomes the home of a music festival that includes among its historic moments the US opera-singing debut of Leontyne Price. It offers fare ranging from medieval music to today's. People who know both Castle Hill and Glyndebourne in England - home of a unique opera festival - say that, as a setting, Castle Hill has the potential of becoming an American Glyndebourne.

Executive director William J. Conner, in fact, decided he would like to see an annual Mozart opera production. To kick things off, he invited Peter Sellars, one of America's most gifted young directors, to stage ''Cosi fan tutte.'' Mr. Sellars, who has just been appointed head of the theatrical activities at the Kennedy Center for the Performing Arts in Washington, is also one of the most controversial stagers today - but provocatively, not anarchically.

Naturally, when a ''Cosi'' set is unveiled to reveal a pink-neon ''Coffee Shop'' sign and kelly-green leatherette banquettes, there is bound to be some kind of reaction, and the opening night audience was divided between glee and derision. Yet, as the evening progressed, Mr. Sellars made it amply clear why he was bringing the action to the '70s. Mozart and his librettist da Ponte were addressing profound human issues, and nowhere is this easier to miss than in ''Cosz.''

The opera is, on the surface, a comedy about disguises and about the nature of faithfulness in women. Two rakish fellows (Guglielmo and Ferrando) plot with a cynical bachelor, Don Alfonso, to leave their betrotheds (who happen to be sisters) under the pretext of war and then return in disguise. They want to prove the constancy of their beloveds. Unfortunately for the men, who end up trying to seduce each other's intended, the women ''fail'' the test. Too often, the opera becomes a comic romp that wanly ''proves'' that women are cherishable but fickle - the darker side of the ''comedy'' that is ignored or missed altogether.

Sellars instantly shows us two bored war vets who have nothing better to do than arrogantly accept a seemingly innocent wager. They swagger obnoxiously, reeking self-confidence in a broadly chauvinistic fashion. By the end of the opera, they are shattered beyond mending, for they learn not only that the sisters are not faithful, but that they have discovered soulmates in the ''wrong'' partners. In the end, convention - which ultimately makes fools of us all - forces them to return to the original marriage plans, and (implicitly) a lifetime of misery. The supposedly ebullient coda of the opera - ''Happy the man who takes all things the right way'' and ''who lets reason be his guide,'' for he will find ''beautiful calm'' in the midst of the world's tempests - becomes a bitter, agonized study in cruel irony, since no one has benefited from this stupid wager.

Too often, Mr. Sellars's sense of humor sinks to frat-house bawd as he tries to give a sense of the physical as well as the metaphysical nature of the relationships being explored. He is obsessed with gesturing, a device that time and again added an unnatural, intrusive element to the proceedings. On occasion, it created images that, when recalled in the characters' bitter confusion of the second act, were truly penetrating. Generally though, singers are never given a chance to stand still and really internalize an emotion. Not all the updated translations jibe exactly with the Italian text being sung.

But none of that can take away from the fundamental fact that Mr. Sellars, who graduated from Harvard four years ago and is still in the first flush of youthful enthusiasm, has thought about this opera, textually and musically. He has ingested it and has then tried moment for moment to elucidate a musical/dramatic point, to make it all tie together.

The final mood, however, is entirely too bitter for ''Cosi.'' Sellars has a long way to go in the matter of self-editing, of weighing every idea to determine if it adds or detracts from the specific moment. And it would be nice to see him attempt an opera production that made all its dramatic and emotional points within the confines of the composer's and librettist's original intentions.

Visually, the Michael Nishball set was handsomely juxtaposed with the natural beauty of the open-air Italian Garden. Mr. Sellars's use of depth - back to the top of a long staircase that leads to the Crane house itself - was consistently effective.

Musically, a huge amount of goodwill was necessary. The singers were mostly Boston-based, with the only standouts being James Maddalena (the levels of anger , bitterness, and frustration that poured out in the second act were frightening), and Sue Ellen Kuzma's remarkably acted Despina - a savvy and abused creature rather than merely a pert chambermaid. Otherwise, the singers seemed unable to make the excessive gestures and movements appear motivated by anything but directorial decree. The orchestra played the uncut score well enough under Craig Smith, yet his homogenized approach to the dramatic side of the music was particularly distressing in the diffused outdoor acoustic. Caramoor

Caramoor, an elegant mansion in Katonah, N.Y., is the home of a summer music festival. In one of its gardens a Venetian theater was built in the 1960s to allow a full-size chamber orchestra to perform. It was in that open-air theater that I heard the sort of delightful concert that has kept music lovers going there for over 25 years. Julius Rudel, former Caramoor music director, was on the podium in a program that opened with Ginastera's ''Variaziones Concertantes'' (1953) - a beautiful, neglected piece by the late Argentinian composer. Mr. Rudel and Andras Schiff joined forces in the Mozart Concerto in B-flat major, K. 456 (No. 18), infrequently heard and enchantingly rendered here: Rare it is these days to find a conductor and soloist who feel every phrase of the music in similar fashion and project it with such elegant spontaneity. Rudel's bracing account of the Beethoven First Symphony closed a model program in beautiful surroundings.

Caramoor concerts run though Aug. 26. ''Cosi'' plays at Castle Hill tomorrow and Saturdays at 8:30 p.m.