YOU MAY NOT have heard of David Pownall. But he is about to become an internationally produced playwright of impressive dimensions: nine different productions of his "Master Class" are scheduled in seven countries over the next year, including the American version that opened at the Eisenhower Theater last night.

Pownall seems pleased but by no means overwhelmed by this apparent success -- perhaps because his years of gradual achievement in the theater have taught him how ephemeral glory can be. The play, certainly, is not what one would immediately forecast as an international hit -- a dramatization of an imagined encounter between Dmitri Shostakovich, Sergei Prokofiev, Joseph Stalin and Marshall Andrei Zhdanov in 1948. The subject is artistic repression, power, courage. It is a historical play inspired by the Musicians' Union Conference of 1948, but do not expect facts. While Pownall says the facts he uses are accurate, he claims the dramatist's right to sow dry information on the fertile turf of his imagination and reap the harvest.

The outrages of the conference have been amply documented, most recently by Galina Vishnevskaya in her just-published autobiography, which Pownall has just seen. He read one biography of Stalin, but aside from the transcript of the conference he consciously avoided doing research, letting his concept of the two composers be shaped by listening to their music. He was not pleased when one media organization sent a Russian expert rather than a theater critic to review the play.

He did visit Russia, after his first attempt at writing the play proved unsatisfactory. "I hadn't been able to catch what I felt when I read the transcript -- a catch in the emotions that both alarms and excites you. I went to Russia to try to find it, and it was just a little bit of gossip that I picked up which gave me my key. It was a story that Marshall Zhdanov had offered to give Prokofiev a piano lesson. I don't even know if it's true -- but that inspired the idea of this meeting."

Pownall, who looks like Michael Caine playing the part of a bespectacled, slightly rumpled playwright, comes from Liverpool, which is evident from the way he pronounces, say, "rugby" ("roogby"). He took a long route to his current occupation, spending 10 years after his graduation from the University of Keele as a personnel manager, three years for the Ford Motor Co. and seven in Northern Rhodesia, now Zambia, working for the company that ran the copper mines. It was in Africa that he got involved with theater, after writing two novels in his off-hours. The seriousness of the British expatriate amateur theater is legendary, and the one Pownall got involved with was no exception. Before long he was writing plays for them, and eventually his bosses asked him to make a choice between his avocation and his job. "My secretary was typing a lot of scripts," Pownall admits.

He decided to throw over the comfortable life of a corporate executive for the impecunious one of a writer, moving his now ex-wife and son back to England. Assuming (wrongly, as it turned out) that a writer should live in a romantically remote area, he took up residence in the Lake District and soon got quite lonely. A traveling theater company, contained in six vans that converted into a stage and auditorium, came through his town; he wrote down the name he read on the vans, sent the company a letter asking for a job, and was soon working for a minuscule salary, putting up posters. By the end of the year the group was performing one of his plays -- "my first professional production" -- and shortly after he commenced his life as a writer.

"Master Class" was first produced in England, prompting a variety of reviews. Both the extreme right and the extreme left loved the play, he says, and the centrists called it "a defense of bourgeois individualism."

"In England the theater is far more burdened with political ideology than it is here, and the fashionable debate tends toward the left-wing view," says Pownall, who describes his own politics as "resenting all government" while believing in the need of the state to support those who can't help themselves. "I've been called everything. The right thinks I'm too sympathetic to Stalin, but my intention was to see him as a human being, who did the deeds of an inhuman mind."