Mstislav Rostropovich music director of the National Symphony, won his fight to fire first flutist Wallace Mann early Wednesday morning after an arbitration panel ruled against Mann.

The decision was announced after a marathon 13-hour session at the Kennedy Center.

The arbitration panel issued a statement that said: "A decision in the matter of arbitration between Wallace H. Mann and the National Symphony Orchestra was announced by the board of arbitration in which a majority voted to sustain the action of the music director not to renew the services of Mr. Mann at the conclusion of the current season. It was recommended that the National Symphony Orchestra Association grant to Mr. Mann the special benefits which were discussed with him.

Mann, 57, has been with the orchestra 32 years. He said yesterday that he would receive "a year in annuity, at $640 or $650 a month, and at 60 I'll go into full retirement. Meanwhile I'll look for a college position or go on a State Department tour of South America or someplace like that."

Mann was one of three members of the orchestra who were sent letters in November informing them their contracts would not be renewed. Mann says that he does not know for sure if he will continue to perform through the Sept. 3 expiration date.

"I've got a health problem that isn't major that I've been putting off too long," said Mann who was the only one of the three to appeal the decision.

Testifying in his behalf yesterday were former NSO conductor Howard Mitchell and music critic Irving Lowens.

Appearing also on the arbitration panel were Rostropovich and David Lloyd Kreeger, chairman of the orchestra, who backed Rostropovich's action.

Mann had sought unsuccessfully to have the arbitration hearings open to the press. The orchestra said yesterday that a written account of the proceeding would be made available within 30 days.

Mann was dismissed under the "musical deficiency" clause of the NSO contract, but the nature of Rostropovich's charges against him has not been made public.