Just how much "acting"should an acting chairman engage in?

That question is currently being hotly debated at the Civil Aeronautics Board as a result of a flurry of activity by Lee R. West, who was designated acting chairman of the board last Wednesday by President Carter to fill in for resigned chairman John E. Robson.

A board source described much of the activity as an "erase Robson" movement by those who resented the credits he has received over the last two years for revitalizing the agency. Robson had come to the board when its policies and procedures were being widely criticized in the administration and on Capitol Hill. The board generally was viewed as too protective of and cozy with, the industry it regulated.

Board sources said yesterday that within hours of being named acting chairman, West fired Constantine C. Menges, director of the bureau of international affairs, and gave several others, including Howard A. Cohen, who had been Robson's special counsel, a half-hour to clear out of their offices.

Menges had already submitted his resignation effective June 30, but expected - as do others planning to leave relatively soon - to assist the new chairman, when he comes on board, in a transition.

Most of the changes made so far were not of a substantive policy nature, although the board on Thursday did give the airlines a month's delay on implementing one of Robson's special projects, a new consumer information program.

In December, the CAB had ordered the airlines to begin providing the public with easy - to - understand summaries of available normal and discount fares to major cities, beginning June 1, in time for summer vacations.

The board now has delayed the start of that program until July 1.

White House sources would say only that West is an interim appointment and intended to be a caretaker until a new chairman is nominated and confirmed. The President is expected shortly to name Alfred E. Kahn, an economist and current chairman of the New York State Public Service Commission, to head the board.

West, a Democrat, was a former Oklahoma state judge named to the CAB by former President Richard Nixon in November, 1973.

The current White House had little choice in naming West acting chairman after Robson left April 30. Richard J. O'Melia, a Republican, had submitted his resignation as vice chairman to the President so that the President could name his own person. In any case, O'Melia could hardly serve as acting chairman since he will be in London during the next six weeks, participating in the British - U.S. talks seeking a new air treaty between the two countries.

Both of the other two members of the current board are scheduled to be replaced by the President. The term of R. Tenney Johnson, a Republican, expired in December, G. Joseph Minetti, a Democrat who has been on the board for 21 years, turned 70 last month and would need a presidential waiver to remain on the board. West was not available for comment.