The Maryland Racing Commission declared yesterday a moratorium on Sunday thoroughbred horse racing through 1980, in the wake of mounting opposition from civic and religious groups and members of the Maryland General Assembly.

Commission Chairman Bob Banning said in a release yesterday, "Before a Sunday program would be reinstituted by the commission, we will hold meetings to receive constructive suggestions the community residents, members of the General Assembly, horsemen and the racing associations."

The commission's decision may result in the death in the legislature of several proposed bills forbidding horse racing on Sundays.

Sunday racing in Maryland was introduced at Laurel during its last meeting. The six-week experiment met with mixed results. The horsemen felt the experiment was a success, but Laurel management, which had hoped for at least a $1,250,000 average handle, was less enthusiastic.

Bowie was the next to request Sundays dates from the board. The board granted the race track Sunday programs, the first of which was to be held Jan. 27. But the state attorney general ruled the board failed to adequately notify the public of its hearing and must hold a new one. The setback came the same day that the civic and religious groups testified in favor of several bills forbidding Sunday racing before the House Ways and Means Committee.

Pimlico, which had been enthusiasticly anticipating Sunday racing during its meeting, withdrew its request for Sunday dates. Pimlico faced strong community and legislative opposition, led by House speaker Ben Cardin (D-Balto. City), on the proposal. Pimlico General Manager Charles (Chick) Lang said yesterday, "Pimlico is in the middle of two areas, one commercial, the other residential. The Sunday racing proposition appeared to be developing into a war between the several factions; the businessmen wanted it, the residents didn't. Our track would have been the no man's land between those two factions. Of course, we wanted it, too, but the price would have been too great."