Mstislav Rostropovich said yesterday that he plans to take a year's sabbatical from his duties as music director of the National Symphony Orchestra in 1984.

He explained that he is arranging his schedule so that he will not be away from the orchestra for an entire season. "We plan to be here the same number of weeks as normal," Rostropovich said in an interview.

The orchestra's executive director, Henry Fogel, said later that in the fall of 1983 Rostropovich will be with the orchestra for "seven subscription weeks, beginning in mid-September and extending into mid-November. Then he will be here for eight subscription weeks starting in January 1985 and ending in May." Rostropovich has averaged 10 or 11 subscription weeks in most seasons.

In addition, Rostropovich will conduct the National Symphony on two American tours during those seasons. He will lead the orchestra on a two-week tour of the West and Southwest in early October 1983 and another tour in March and April of 1985.

Rostropovich, who is now in his fifth season with the NSO, said that he has chosen 1984 for this respite because "that is the 10th anniversary of my new life. I left the Soviet Union on the 26th of May 1974."

Rostropovich said that his first years as an e'migre' from Russia were hectic and sometimes difficult, "but my dream is now coming in my life."

At the time of the sabbatical, he explained, "I will do just as I did when we came in 1974. I will go to London, get a car and drive to Cambridge and ask my friends to meet me there, just as they did before," when he and his family arrived in the West from the Soviet Union. They emigrated following a period of persecution for, among other things, having given shelter to Alexander Solzhenitsyn at their country home. An early haven for the Rostropoviches was the home of the late British composer Benjamin Britten, in East Anglia near Cambridge.

"One thing I am going to do," Rostropovich said, "is apply myself to the Bach suites the six Bach unaccompanied suites for cello and I will probably record them. It will be a sabbatical to work, not to rest."