Mstislav Rostropovich held a press conference yesterday afternoon to protest the fact that his sister, Veronica Rostropovich, who has played the violin with the Moscow Philharmonic for over 20 years, is not being permitted to accompany the orchestra on its current tour of the United States and Canada.

Rostropovich said he believes his sister is the only member of the orchestra to be sigled out in this manner. He said she played with the Moscow Philharmonic when it came to this country some years ago. The orchestra is scheduled to play in the Kennedy Center on Feb. 24.

Relating the ban on his sister's travel to the Soviet government's stripping him and his wife, soprano Galina Vishnevskaya, of their Russian citizenship last March, Rostropovich said, "From that time on, we were vilified in the Soviet press. But the powerful individuals who manage the government, supposedly in the name of the people, did not stop there.

"They are now persecuting my sister, my only close relative left in the Soviet Union." He said that his sister's professional position in the orchestra has always been good, adding:

"I spoke with her on the telephone to Moscow two days ago. Her voice was very disappointed that she is not traveling with the orchestra, but for a month now, she has had no work. This process is often the first step in our system: not permitting people to go abroad."

He said he asked his sister if it would be better if he did not say anything about the situation, "but she said, 'No, it would be better if all words are spoken true about our lives.'"

Rostropovich said Soviet citizens who are prohibited from traveling abroad are "marked as politically unreliable. A person to be avoided by his countrymen. The future of such a person is bleak, personally and professionally."

A spokesman for the New York office managing the tour of the Moscow orchestra said yesterday that the office simply procured visas for the names of the players submitted to it from Moscow and that it had no way of knowing if other members of the orchestra are not traveling on the tour. The cultural officer of the Soviet Embassy was not available yesterday for comment.

In the opinion of experienced managers of the entertainment world, there have been other occasions when a member of a Soviet group has been denied permission to make a tour. One manager said he knew of times when artists of Soviet ensembles had been taken from planes at airports just before departure in what appeared to be acts of political pressure.

Rostropovich, who will be 51 in March, said his sister is a year and a half older than he, with two sons, ages 9 and 21. Her husband teaches Chinese. "She does not want to leave her country," he stated emphatically. "She has no thought of remaining in the West.

"Now," he added, "she is like a hostage. Maybe they (the Soviet government) think that I will not speak so openly, maybe I will speak a little 'diminuendo.' But if I am quiet for one time, then I must be quiet forever.

"Twice in the past, I have asked friends of mine, one in Europe and one in this country, if it was possible for them to speak to the Soviet ambassador. I speak to them very confidentially -- I think it is very bad to make something against my sister. They say they will do their best.

"I knew what was happening from many Soviet friends who have come to this country, who have said, 'We have a feeling that your sister is not coming with the orchestra.'

Asked if he though there might be some reaction to his statement, Rostropovich said, "I am not waiting for an answer for me. And my sister does not always tell me these things.

"Of course an answer will be coming to my sister." The harassment could end, he said, or "maybe the Soviet government will say, 'He makes more statements about us, so we will make tighter restrictions."

"I do not want to make waves." the concluded. "I want to make very peaceful." At the end of the press conference, Rostropovich read his prepared statement in Russian for broadcast over the Voice of America and Radio Free Europe.