Rejecting an unfair labor practice charge brought by the teachers' union, the D.C. Board of Labor Relations upheld yesterday the right of the city school system to appoint the commitiees that select textbooks for use in Washington classrooms.

The decision ratified the school adrninistration's edict that ended a timernonored practice under which the Washington Teachers Union, an AFL-CIO affiliate, dictated the membership of the committees, thus dominating the book-selection process.

School Superintendent Vincent E. Reed praised the labor board's decision, saying it "upheld the responsibility of the Board of Education and the superintendent -- and not just the union -- to choose those who select textbooks."

William Simons, president of the union, could not be reached last night for comment.

The decision stemmed from an unfair labor charge filed by the union early in 1977. The union complained that Reed, on his own, had ended a practice dating back as far as 1968 under which the union could approve or reject those nominated by the superintendent to serve on the book committees. About 300 teachers and administrators serve on the committees.

Reed said he was determined to end the union's appointment monopoly just as soon as he found out about it. The union complained that the action undermined its ability to deal with working conditions.

Arnold Ordman, who conducted the labor board's hearing in the case, said in his official report that he could not accept the union's position.

"The critical feature of the federal (and District) labor law in the bargaining area is that the obligation to bargain is confined to matters concerning wages, hours and other terms and conditions of employment," Ordman wrote.

Where there is no obligation to bargain, he concluded, management's sir gle-handed action does not amount to an unfair practice.

George Margolies, attorney for the school board, said the union in past years had routinely vetoed the superintendent's appointment of teachers who were not union members. Reed said the school system's challenge to the union position "does not mean we are trying to do away with the union input."

The D.C. labor board deals only with disputes involving municipal departments and agencies.