Mstislav Rostropovich defended yesterday his decision to dismiss three veteran members of the National Symphony Orchestra as "the kind of thing that music directors sometimes have to do."

Rostropovich made his first public statement about the actions last November in answer to a question at a session of the Wolf Trap Associates at the Shoreham.

"It's a normal thing in the life of an orchestra and it's done with orchestras everywhere. I had to make the decision and now we must finish this thing.

"But I promise to you that we would change somebody in the orchestra only if there were a need for a really higher quality."

An appeal by first flutist Wallace Mann is now in arbitration, a process by which Rostropovich could be overruled. The Soviet cellist-conductor referred to this as "an American procedure," with the implication that it is beyond his expertise. "I cannot comment until we see how it comes out."

Arbitration was invoked after a players' committee narrowly upheld Mann last week. The other two musicians dismissed did not appeal.

At the lunch to publicize the orchestra's summer season at Wolf Trap, Rostropovich also discussed his methods of attracting some of the world's leading conductors here as guests. "Friendship is very, very helpful in these situations. Sometimes I make some kind of blackmail."

In attracting as a guest next season Claudio Aboado, music director of Milan's La Scala and the new conductor of the London Symphony Orchestra, Rostropovich said he told him, "If you do not come, I will not be able to play with you on the cello." In a reply, Rostropovich said Abbado told him, "I will come when you agree on the date to play in La Scala." A similar exchange agreement was worked out with the Boston Symphony's Seiji Ozawa, said Rostropovich.

One person asked how Rostropovich manages to keep up his cello technique while conducting for extensive periods. "At those times," he replied, "I played just enough to keep the flame alive. Then when I've got a free time, I work until I get the full blaze going again."

On one issue that provokes occasional disagreement, he was asked, "Sir, is your last name pronounced RostroPOvich or RosTROpovich?" he said it was the former "as in ShostaKovich, but my wife (Soprano Galina Vishnevskaya) is the other way, VishNEVskaya.

"I'd really prefer that everybody would call me 'Slava,' though. If I go into a hotel and call room service and give them a simle name like 'Slava' there's no fuss, and the food is right up. If I say 'Mstislav Rostropovich' I have to spell it cut and the food doesn't arrive until 30 minutes after I make the call."