One would hardly think of Carnegie Hall as an important opera house, but last Sunday it inaugurated its Gala Rossini Opera Festival with a vibrant performance of that composer's little-known ''La Donna del Lago'' (''The Lady of the Lake''). The performance generated more excitement than most evenings at the Met in recent memory.
The obvious reason for the ''festival'' is singer Marilyn Horne, but the primary benefit to concertgoers is exposure to three operas that neither of this city's houses seems remotely interested in presenting. In addition to the opera in question, ''Semiramide'' and ''Tancredi'' will be heard during the season.
Rossini has never been taken very seriously in the United States, particularly in New York. The Met seems to feel his ''L'Italiana in Algeri'' should be a rarity. ''L'Asseido di Corinto'' was done as a vehicle for Beverly Sills' debut and has not been heard since. The City Opera has at least given ''Il Turco in Italia'' and ''Le Comte Ory'' a chance.
So Carnegie Hall is offering a service to music lovers. And it is offering Miss Horne, one of our most important singers, a showcase she has been consistently denied at the Met. Agnes Balsta had been originally announced but withdrew, so Frederica von Stade replaced her. Thus, the New York principal cast was that of the US premiere production last season at the Houston Grand Opera - Misses Horne and von Stade, Rockwell Blake, and Dano Raffanti.
The opera is a splendid showcase for five grand singers. It treats the Sir Walter Scott story of the same (English) title in an opera seria format - a string of imposing arias tied together with action-forwarding recitatives. The arias range from good to glorious, with some stunning ensembles, duets, and trios along the way.
She was the star of the evening - a magnificent voice wedded to a superlative technique and a thrilling sense of how to communicate in multifac-eted and thrilling form.
The Orpheon Chorale sounded twice as large as most groups its size. And the conductor, Donato Renzetti, at the helm of part of the excellent American Symphony Orchestra, showed himself to be a superb Rossinian in his US debut. His is the sort of superior style that should be the norm in New York's opera houses.
But beyond these artists, the evening was more of a problem. Miss von Stade, for instance, with all her musicianship and control of florid line, displayed a basically monochromatic and small mezzo-soprano that thins out alarmingly in the often-used upper register. From her and other singers there was little sense of an important voice reveling in the joys of great singing, which is - as Miss Horne so gloriously demonstrated - the cornerstone of the bel canto tradition.
The remaining performances in the series are on Jan. 10 (''Semiramide,'' starring Montserrat Caballe) and May 22 (''Tancredi,'' with Ileana Cotrubas). Prague Symphony
The ''draw'' for the Prague Symphony concert at Carnegie Hall last week was violinist Eugene Fodor playing the Brahms concerto. It passed uneventfully - a just-competent job from a player of potential who has yet really to settle down and give the listener true insight into the music he plays.
The joy of the concert was a melting, lilting, understated Czech performance of Dvorak's ''New World'' Symphony. It was not bloated with melodrama, distorted to serve the needs of an interpretive conductor, or made to sound merely bland or uninteresting. Rather, Jiri Belohlavek offered an effortlessly graceful reading, with an orchestra of high caliber. The strings in particular had a lovely, woody hue, and throughout, there was nothing less than excellence about the ensemble. For once, the ''New World'' sounded fresh and new - most unusual and welcome for such a hackneyed work. TBerganza recital
Teresa Berganza's Carnegie Hall recital - her last in a series of appearances around the country - was incandescent. The beloved singer is a superb vocal actress and a great artist. She does not so much project songs as inhabit them.
Mussorgsky's ''In the Nursery,'' sung in Russian, found her, with a minimum of histrionics, becoming now a young child, now an overbearing, overweight nanny , now an elegant, aloof mother. Her varieties of grief and suffering in the six Granados songs that opened the second half were convincing without being overbearing or overcalculated.
There is no artifice to her heartfelt art. And her generosity toward her audience was unusual. After the program, which opened with Haydn's cantata ''Arianna a Naxos'' and closed with six Ernani Braga songs, Miss Berganza offered eight encores, ranging from arias to the pop song ''People.'' The audience let her know vociferously how much it appreciated her artistry. Yepes's 10-string guitar
Guitar concerts in Carnegie Hall can be a frustrating affair. Narciso Yepes brought his 10-string invention there last Thursday, and suddenly it was not a problem hearing that instrument in that space.
His guitar fills the hall with sound. The musician who plucks it is one of the finest in the world today. The second half of the program was devoted entirely to 20th-century works, an intriguing survey of music - for an apparently limited instrument - that was at once engrossing yet challenging. Of greatest interest were Eduardo Sainz de la Maza's ''Laberinto,'' with its jazzy undercurrent, and Leonardo Balada's supremely virtuosic, exciting ''Analogias.''
Mr. Yepes, who appears to be not much larger than his oversize instrument, is a selfless musician, putting the music before his personality in what could serve as the ideal of any performing artist but so rarely is. One left his recital stimulated and elated, with nary a thought as to the potential limitations of the instrument, dynamically or musically.