JUST A FEW years back, Harvard used to celebrate twin rites of spring: a student demonstration in the Yard, and a Mozart opera at Leverett House. It was too good to last. Some claimed the demonstrations helped send Nixon to the White House. I guess the operas must have helped send Leverett's Master to the New York City Opera. And there matters rested until this year. So with Watergate behind us, as the saying goes, a Mozart revival was clearly past due.

Despite its high quality, the Summer School's New Opera Company doesn't really fill the need--its version of The Marriage of Figaro is a concert one, with no recitatives, few choruses, and singers standing up in tails. Much of the comedy inevitably gets lost. Beaumarchais's original version, first produced just five years before the French Revolution, was regarded as dangerously subversive because it concerned a valet's just victory over his adultery-minded master.

Lorenzo da Ponte, Mozart's librettist, had to get special imperial permission before the opera could be produced, and though da Ponte mitigated Beaumarchais's social commentary he left intact his characterizations, characterizations that Mozart fleshed out into some of the most convincing in music.

Mozart put some of the lost irony back into the music, and it could be argued--although perhaps not too convincingly--that having just the music makes some of the ironies clearer. There are beautifully ambiguous moments like the quiet, harp-like string passage-a rebuke to the Count, a relief to the Countess--when Susanna comes out of the closet in the second-act finale. And director Earl Kim's simple conducting and quiet, steady beat make it easier to see why the citizens of Prague, wiser than the Vienna court which accorded Figaro only a moderate success, adapted its tunes for popular dances.

THE NEW OPERA Company runs into occasional problems. John Davies doesn't really have the voice for Bartolo's lowest notes. Diana Hoagland more than rises to the occasion of the Countess's big third-act aria, but some of her earlier attempts at acting seem a good bit closer to Lucia's madness than Rosina's anger. Sunday night's orchestra didn't seem to approve of them, either--the strings swung briefly out of tune for the introduction to her first aria, something that didn't happen again until the whole orchestra--previously more than competent--began to fall apart, shortly before the end of the last act.

It also seems as though more impeccable financial strictures might have deterred the Summer School from underwriting a professional operatic production. Thomas S. Crooks, dean of the Summer School, said yesterday that it was nobody's business how much the School had given for the production, but it must have been thousands of dollars. It's nice to have a Cherubino sing Voi che sapete--particularly as well as Susan Larson sings it. But we also know that student artists at Harvard--though their performance wouldn't be as good as the New Opera Company's--could find good uses for some money, uses that involved larger numbers of students. And we know that Harvard's deficits and tuitions keep going up. Mozart was a simple man: he would have understood.

As it is, since most of this Figaro's singers are fine--particularly Judith Hubbell as Susanna and David Arnold as Figaro--the opera seems more complete than it might, even with the drama truncated. A concert version is certainly better than nothing: like the post-Watergate era, Mozart's music balances a multitude of sins.