By the time Mstislav Rostropovich made his first American tour in 1956, he had already won international acclaim and the status of a superstar. One young professional cellist, upon hearing that the Russian had obtained a two-year emigration visa in 1974, left his wife and cello behind in the States, hopped a plane to England, and for the next few months spent days seeking out his demigod and nights sleeping on park benches and in public toilets. Today, wherever Rostropovich plays, tickets sell out within hours. Only one week after he announced his decision to defect, the National Symphony chose Rostropovich to succeed their outgoing musical director and conductor.

For the 1200-plus people who packed into Sanders Theatre last Saturday afternoon to watch him in action, Rostropovich dissolved any mystery surrounding the origin of his overwhelming popularity.

The occasion was a master class with two undergraduate cellists, Rostropovich's only public appearance at Harvard during a five-day stay at the University. From the moment he walked onto the Sanders stage, whether talking or gesticulating or demonstrating, Rostropovich won the rapt attention of his audience. Wildly waving his arms to illustrate musical points and likening performers' bad habits to sausages, pollution and clumsy love, Rostropovich repeatedly exhibited what a superlative musician can offer a student and an audience, even without his instrument.

And when both cello and audience are out of sight and the world-famous cellist sheds the veneer of the grande artiste, Rostropovich projects an idiosyncratic blend of energy and joie de vivre. As evidence one need only glimpse at the man after the master class, hulking like a Russian bear in his furry coat, dignified, prematurely gray and balding, with a protruding lower jaw, pulled along by his prize possession and constant companion, "Pooks." Pooks, the effete miniature dog who accompanies Rostropovich everywhere he goes, was insisting that they be fashionably early to the post-class reception.

By now, Pooks has grown accustomed to tea and cocktail parties, and with all the attention he gets at them, it's no wonder he's anxious to get there early. "I love my Pooks more than anything else in the world," Rostropovich told one of the guests, and apparently he wasn't exaggerating. Rostropovich interrupted his tour of England in the summer of 1974 to visit Pooks, who was in quarantine in the finest animal infirmary in France.

Yet Rostropovich is not immune from the egotism stereotypically associated with superstars. Last week, when a Boston Symphony representative failed to pick up Rostropovich at Logan Airport, the Russian became infuriated and decided to seek revenge. Without a word of warning, he hailed a cab with cello and Pooks in hand and asked to be delivered to the Colonnade Motel, a block from Symphony Hall.

Pandemonium broke out in the managerial offices upstairs at Symphony since no one could find the soloist, who was scheduled to rehearse with the orchestra two hours earlier. When a Harvard official finally located him after remembering that Rostropovich had stayed at the Colonnade on his last trip to Boston, the cellist sat sulking and refused to go to the rehearsal. "He just wanted to play prima donna when he wasn't met at the airport. He specifically didn't go to Symphony, even though he could have been there 20 minutes before the rehearsal. He happens to be very temperamental," the official, who asked not to be identified, said. Only after a barrage of pleas did Rostropovich agree to rehearse with the orchestra, three and one-half hours behind schedule.

But on Saturday Rostropovich conveyed only affection, whether he was fondling Pooks, talking about his penchant for Chinese food, or embracing and kissing everyone in sight, as he did at Saturday's reception. The joy he shows today contrasts with the sad memories he has of the Soviet Union, where his refusal to participate in what he calls "officially organized persecution campaigns" cost him his professional and social freedom several years ago. "I lived," he says, "according to my conscience and my heart."

Rostropovich's outspoken support of intellectual dissidents put him in constant trouble with the Soviet government. He was barred from travel abroad for three years. His refusal to sign letters denouncing Andrei Sakharov led to the onset of what the cellist calls "silent torture." When he gave refuge to his friend Alexander Solzhenitsyn, who spent four years in Rostropovich's home, the cellist's musical life in the Soviet Union was squelched. Radio announcers were not permitted to mention his name. At one point all his concerts were cancelled. Once, in a small town, Rostropovich saw men obscuring posters for his concert, on orders, they said, from party leaders. And when he played, the houses were often half-filled. "People were afraid to come."

"Our government was systematically corroding and stifling our artistic life," Rostropovich said last year. "They wanted to prove that we did not exist. We were treated like lepers. We lost our identity. It was like looking into a mirror and not finding your reflection. In Russia," he said with characteristically vivid imagery, "if one blade of grass grows higher than another, they send in bulldozers to trim it down."

Con Espressivo

A master class is unquestionably the most pressured forum for a student and teacher working together. A student must perform for teacher and audience and is expected to adapt a master's suggestions to his playing with little time to digest the advice, let alone work on it. A cello teacher, on the other hand, must gear his advice to the student so that the audience of cellists and non-cellists, musicians and non-musicians can profit from the class.

At times on Saturday Rostropovich met the challenge by hamming it up for the audience rather than concentrating on valuable musical criticism. One music professor said she felt like she was watching a tape of the Johnny Carson Show. Rostropovich never severed his communication with the audience. Colorful metaphors abounded. At one point in the Haydn D major Concerto, a theme appears twice in the score: once in the low, masculine register of the instrument and then in the bright, upper register. "Why, all of a sudden, does the theme appear in the upper register?" he asked after Gregory Colburn '79 had played the passage. And without waiting for a reply, he added, "Because there was not enough air in the low register. It is as if you open the window. It must have plenty of sunshine." Rostropovich turned his head away from the audience toward Colburn. "You opened the window--but in New York City."

When Rostropovich concentrated on musical points, his suggestions effected noticeable improvement in Colburn's playing. Allowing your imagination to be your guide, Rostropovich told Colburn, will eliminate technical difficulties. The Russian asked Colburn to describe the music he was about to play before setting his bow on the strings. "When you truly understand the music, the desire to play the music will awaken itself in you. Your imagination must always be your teacher. It must teach you before you've sat down at the instrument."

The highlight of the master class was the confrontation of the 49-year-old Soviet emigre, who is often called the world's greatest cellist, and senior Yo-Yo Ma, who has already had a remarkable career in his own right. In fact, until Rostropovich switched to Columbia management last year, he and Ma were two of only five cellists in the world under the management of impressario Sol Hurok.