The Washington Opera brought Bellini and Donizetti to its Kennedy Center subscribers over the weekend as it opened the first of four performances each of Bellini's "I Capuleti e I Montecchi," and Donizetti's "Don Pasquale."

Seeing the two within a span of 20 hours placed an unusual emphasis on differences in approach, and underscored some of the happiest elements of both. In each, the audiences heard some superb singing and saw some outstanding acting. And in each, the choral singing, prepared by Mario Salerno, had a polish and stylistic tone not often heard in previous Washington Opera productions.

Both operas were written for the most famous stars of the 1840s. Both demand, for their ultimate effect, a kind of vocal style and technique not widely available these days. Yet in Bellini's version of the story of Romeo and Juliet, Tatiana Troyanos as Romeo quickly established and maintained a level of artistic song that satisfied every requirement. Nothing illustrated more overwhelmingly her complete identification with the role than the hushed sob that escaped her when the body of Juliet was uncovered in the final scene. Earlier, she had easily and liberally dispensed both tone and technique in the grand manner. And her carriage and posture in a male role were among the finest things to be seen in this kind of opera.

inda Zoghby's Juliet was deeply affecting in her sensitive singing, exquisite tone and the nuances with which she shaded the anguished character. Her posture, however, was poorly conceived, especially in the early scenes where she continually looked as if she had a violent gastric pain.

Julien Robbins, a young baritone singing Lorenzo, was impressive both for his excellent resonant voice, and his distinguished use of it. The role is not a strong one, but Robbins made it very effective. Harry Dworchak made what he could of the unbelievable cruelty of Juliet's father, who is correctly described in the opera's final line as "ruthless." These is little to be said for Antonio Savastano's Tebaldo, or Tybalt. He was stiff in movement, leaden in sound, and totally dependent on conductor Nicola Rescigno. Even that did not keep him on beat all of the time.

Rescigno, who knows everything about this kind of opera, conducted in expert style.

Stage director Christopher Alden moved the action to the 1830s. Since the libretto is often scarely more than cardboard, there seemed little reason for the switch-which only made it more difficult to remember that it was a version of the famous love story. The costumes would do very well for "War and Peace." There was no set. A single large triumphal arch was ineffectually used for all backgrounds. A battle scene was to laugh.

Thanks to the several-sided genius of Paolo Montarsolo, Donizetti's best comedy opera looked and moved with great zest and wit. And for some moments at the end of the first scene of the last act, there was a flourish of brilliant prestissimo singing from Montarsolo in the title role and his deft companion, Richard Stilwell as Dr. Malatesta, that stopped the show and won an encore.

Montarsolo as stage director has put "Don Pasquale" on a solid footing as lively comedy that is not farce. Its principals behave like well-motivated human beings, if somewhat greedy or foolish. Much of Montarsolo's thought and direction obviously rubbed off onto his fellow principals. Both he and Stilwell sind handsomely at every point.

As far as the requisite florid technique and legato lines are concerned, all four principals sang very well indeed. Barbara Daniels had the pert, deceptive Norina completely in control, and gave her a fair amount, though not enough, of subtle vocal nuance. Her voice is a bit larger than customary in the part, though not at all more than it can use. At the top, she put on a sharp edge that would be more effective if checked a bit.

Rockwell Blake had no problems with Ernesto's range or fluency. But his famous serenade in the last scene had all the subtlety of a metronome. The element of charm, in tempos and phrasing, was the central factor that needed more emphasis in the show. Conductor Theo Alcantara is efficient but not very interesting. Patricia Collins' lighting was more effective in "Don Pasquale" than in the Bellini, but opening night wrinkles may by now have been smoothed out. CAPTION: Picture, Paolo Montarsolo in "Don Pasquale"