First flutist Wallace Mann showed up for rehearsals with the National Symphony yesterday morning as he has for the past 32 years. Leaning against a water cooler during a break in the performance of Verdi's tumultuous Requiem, he talked about the efforts of music director Mstislav Rostropovich to get rid of him and of the ruling of a 15-member player board last Friday that Rostropovich should not.

"You know, there really isn't any hostility. I had never even heard a complaint from him until last November, when he called me in and said he wanted me to go. Different people have different tastes."

Unlike two horn players given notice at the same time, Mann, who is 55, said he decided to challenge the firing. "At first I was willing to listen to offers, but it was clear before long that they weren't going to come through with enough (money)," he said.

As of yesterday, Mann had not been told whether the NSO would appeal th decision of the player board to a special arbitration board of ultimate authority.

Rostropovich declined comment, but orchestra manager Robert Noerr said that an appeal will be made.

"I'm just going to continue playing the flute, as I have done successfully for the last three decades," Mann said before ambling back to his seat on stage directly in front of Rostropovich.

It was at a four-hour sessionin the Kennedy Center's Green Room Friday that Rostropovich presented his case for replacing Mann to the player board. One person present said that Rostropovich did not specifically critique Mann's playing, but "spoke of the musical quality of the orchestra as a whole."

The result of that meeting was an 8-to-7 secret vote supporting Mann that was said to take management by surscribed Rostropovich as "extraodinarily disappointed" by the vote.

Had either management or Mann received 10 votes of the appeals board, the decision would have been final. A similar board upheld management in anothe rdismissal in the early 1970s.

Clarinet player Lawrence M. Bocaner, chairman of the board that heard Mann's case said in a statement: "It is the sense of the committee that there are some musical problems, but the alleged musical deficiencies are not of an order that would require an action of this magnitude, and indeed, may be remediable." The group included a blance of first-chair players and othe rmusicians.

It is not clear when an arbitration board can be formed to hear the case. Rostropovich goes abroad for an extended period on March 10, and Noerr would like to have the matter settled before then, he said yesterday.

Two arbitrators would be chosen by the orchestra and two by the union. The remaining three would be nominated by both sides, but would have to be unanimously approved by the initial four members.

A random sample of musicians during the break in yesterday's rehearsal showed support for Mann.

Said one, "I'm surprise I that seven members upheld the orchestra. Wally is a beautiful player."

Another observed, "I guess this Mann's dismissal is orchestra building and that's the business. But the point is that Dorati Antal Dorati, Rostropovich's predecessor) could pull it off with so little camage to people."