Paolo Montarsolo describes himself as a "basso-buffo." And, as such, he is one of the leading exemplars of a mode of singing and acting that has its roots in the 16th-century Italian conventions of the commedia dell'arte .

That was about a century before the first opera was composed. At first those comic roots had their greatest influence on European playwrights-such gaints as Moliere. But it is in opera where we encounter them today in their least adulterated form, particularly in the Italian opera buffa.

A layer of superfluous hokum, however, has accumulated on many of these works over the years, much as dust, wax and varnish come to distort old master paintings. And the indefatigable Montarsolo has an almost missionary zeal for the cleaning away of these impurities in the performances of operas of Donizetti, Rossini and, to some extent, Mozart.

Just such a production is what he is aiming for in today's opening at the Kennedy Center of Donizetti's "Don Pasquale."

"This is one of the real masterships," he declares in his serviceable, if sometimes quaintly erratic English. Under the aegis of the Washington Opera, Montarsolo will both direct and play the demanding title role for four performances.

"Tradition has obscured the understanding that 'Don Pasquale,' for instance, is really quite deep. The four main characters are human beings and the composer thought of them that way." It is one of the last of the 60-odd operas Donizetti created (both text and music are his); and though not performed as often as his "Lucia," "Don Pasquale" is probably his most widely admired work.

Too often the "buffo" has been interpreted too literally and has come out as buffoonery. The result is a gagoriented humor more in the style of Bob Hope than that of a serious actor or singer trying to get beneath the surface of, let us say, Falstaff.

True, the commedia dell'arte antecedent of most of Montarsolo's buffo roles is a stereotype: Pantalone, a wealthy, foolish Venetian merchangt. But in the best operatic incarnations, the basso buffo parts have individual human dimensions that leaven the oafishness with sympathetic qualities.

"All of them have a face-saving measure of dignity," says Montarsolo. "After all, Don Pasquale is a man of great means who takes on a foolish marriage to a young girl. Likewise, in "The Barber of Seville' you must not forget that Dr. Bartolo was not a clown, but the leading citizen of Seville." He agrees with the reminder by the late Ernest Newman that "Pasquale, for all his amorous foolishness, was a gentleman in an epoch when good breeding still counted for something."

"This is a real disaster for the old man," Montarsolo continues. "He is sincere about what he is doing, and he is hurt in the end. I remember a production I saw once in Salzburg in which everything was done for laughs, and all of this side of it was lost. And then there was the time in Spoleto several years ago when the opera was set in fascist Italy and Ernesto (Don) Pasquale's naive, unwordly nephew) is a black shirt."

Assuming its proper role at the pinacle of Italian opera, it has been Milan's La Scala that has led the way in rethinking the buffa style. Washington first saw the results in 1976 when La Scala brought to the Kennedy Center a production of Rossini's "Cenerentola" under its music director, Claudio Abbado. In this version of the Cinderella tale, the wicked stepmother is transformed into the pretentious, stupid Don Magnifico, baron of Montefiascone. Montarsolo's performance was described by one critic as "brilliant." Asked about his approach, Montarsolo said that "you must not forget that though he is foolish, he is also a baron.

"Here in Washington today we are trying to do 'Don Pasquale' just as it would be done at La Scala. Because we faced up at least 10 years ago to the need to find a way to do opera buffa, Italy is well ahead of the United States in this regard. And we Itallians must teach a little. What we did was simple. We decided to do the works as they were written-more and more Donizetti, for instance, and less and less horseplay."

To make his point, he leaps from a sofa in his lively body English, grabs a round tray from a nearby table and mimics the way it was traditional to pat the girl's fanny in "The Barber," by turning and gently tapping the tray on his own behind. "This could be funny, but it was not Rossini," he declares.

The tall, lean 54-year old basso looks more like Maurice Chevalier than a fatuous old goat of a basso buffo. "I must admit that my figure is not the standard basso body. In fact, I have to use a little padded stomach for Don Pasquale," he says.

Montarsolo's career has taken many unconventional turns. "I almost didn't become a singer at all," he relates. "It really had never even occurred to me until my late teens. It was near the end of the war, and my family had moved from Naples into the near countryside for protection against alled bombs. And I was singing in the shower one day some of the music I had picked up from La Scala radio broadcasts. The piano teacher who lived next door overheard it and rushed in later to say, 'You know, Paolo, you may have voice.'

"Eventually I started taking lessons, but meanwhile I got a job as a bookkeeper and started work on a degree in economics. Then in about 1950 I went to Milano and entered a school connected with La Scala. There were a number of us there whose careers started slowly and developed late." He made his debut at 31, an age at which some singers' voices are already going downhill.

Although he has sung an amazing 169 roles ranging from "Don Pasquale" to "Rosenkavalier" to "Wozzeck," it was by accident that he became master of opera buffa.

"In the school we specialized in 18th century comic operas, mainly because we did not have a chorus and neither did they," explains Montarsolo. "And since I was the only bass and they all had basso buffa parts, those roles fell to me." He modestly failed to mention that another reason is that he is a splendidly adroit and inventive actor, which is an essential for such parts.

This acting skill eventually led him into the dual jobs of star and director at the same time, which is rare enough in the theater and still rarer in opera. Few singers have ever tried directing until after retirement from the stage, something that Martarsolo is not even close to. "The only problem with doing both at the same time is that you have to speak a lot; speech, particularly in a foreign language, is not good for the throat. The advantage is that I understand the problems of the singer better that most directors and we get things done faster. Many directors feel they are not earning their pay if they send the singers home early. I regard it as a compliment."

For so prominent an Italian singer, he has sung surprisingly little Verdi. And at times he sounds like he has spent his career fighting against Verdi's domination of Italian opera. He makes it sound like a personal triumph that Abbado several years ago broke the unspoken rule that the Scale season must open with Verdi, and performed Rossini's "The Italian in Algiers" instead.

Yet there are roles he has missed. "It never occurred to me until awhile ago when I was at the Paris Opera, and the director, Rolf Liebermann, asked if I had ever sung Verdi's Falstaff. I had to say no. But the truth is, that if the offer comes, I certainly might." CAPTION: Picture, Paolo Montarsolo: "Here in Washington, we are trying to do 'Don Pasquale' just as it would be done at La Scala." By Ken Fell-The Washington Post