President Reagan has decided not to increase the number of U.S. military trainers in El Salvador beyond the current self-imposed limit of 55, White House spokesman Larry Speakes announced today.

Speakes said Reagan made the decision Thursday. He added that Reagan has not yet been given options on possibly increasing the number of non-training military personnel in the U.S. contingent in El Salvador.

Earlier this week White House officials said the administration might increase the number of Marine guards and other military personnel not directly involved with training. There is no limit on such personnel.

Speakes also announced today that the National Bipartisan Commission on Central America will hear from former presidents Gerald R. Ford and Jimmy Carter at its next round of meetings Aug. 31 and Sept. 1.

The commission, chaired by Henry A. Kissinger, will also hear at some future date from former president Richard M. Nixon, Speakes said.

On Aug. 31, he said, the commission will hear from Ford, two former secretaries of state, Cyrus H. Vance and Alexander M. Haig Jr., and Thomas C. Mann, a former ambassador and undersecretary of state.

On Sept. 1 the commission will hear from Carter, former secretaries of state William P. Rogers and Dean Rusk and Sol Linowitz, former ambassador to the Organization of American States and a negotiator of the Panama Canal treaties.

Besides Nixon, former secretary of state Edmund S. Muskie is to address the panel later.