The Reagan administration is considering a substantial increase in the number of military advisers in El Salvador so that more "on-the-job" training can be provided to Salvadoran soldiers, administration officials said yesterday.

Some officials want to more than double the current contingent of 55 trainers to 125 or more, while others are talking about smaller increases, the officials said. There is also discussion about allowing the trainers to carry weapons and take a more active role in the field.

"Right now we're just prolonging the agony," one Pentagon official said. "Time is not on our side, and the longer you don't confront the problem, or train them so they can confront the problem, the worse it becomes."

The 55-adviser limit never has been enacted into law, and many Pentagon officials say that they believe it has taken on unwarranted significance. "If we had said 85 two years ago, then 85 would be the holy number now," one said yesterday.

But President Reagan, seeking to reassure those who fear a deepening U.S. involvement in Central America, has said that he does not see a need for more trainers or troops in El Salvador.

A White House spokesman said last night that the president has no Pentagon request for more advisers under consideration.

Consideration of an increase in the U.S. contingent in El Salvador comes as the administration is preparing to escalate its military presence in other parts of Central America. The Pentagon is planning a months-long series of exercises in Honduras and off the coast of Central America, and the carrier USS Ranger is nearing the region's Pacific coast with eight other ships and 70 warplanes.

The U.S. military presence, which now includes at least 300 military personnel in Honduras, is intended to intimidate the leftist government of Nicaragua, to discourage it from sending arms to insurgents in El Salvador and to show U.S. support for friendly governments in El Salvador and Honduras, officials have said.

The United States also is training Salvadoran soldiers to help them combat leftist guerrillas in their own country. Some training has occurred in the United States, and about 1,000 Salvadoran troops are now being trained by 125 Green Beret soldiers in a new camp in Honduras.

Congress is considering writing the 55-adviser limit into law, but the 1984 money bill that would contain the restriction has not been enacted. Some administration officials believe that the number of advisers should be increased to a level they consider more useful before Congress acts.

"You put more trainers into Honduras, and nobody says anything," one official said. "You put more trainers into Salvador and it's escalation.

"To add one trainer in El Salvador everybody thinks it's Vietnam," the official continued. "Fifty-five is a ridiculous figure; it's a ridiculous subject and too much has been made of it."

On the other hand, officials say that an increase could provoke considerable criticism in Congress and elsewhere. Part of the current debate centers on whether the increase is worth the political cost. Some officials would rather encourage Congress to provide all the funds for training outside the country that Reagan has requested and will request in the 1984 budget.

"If the $110 million currently being requested was provided, more of the training could be done outside Salvador, and you wouldn't need so many trainers in country," one said yesterday.

However, Pentagon officials say their advisers in El Salvador can do training different from the cadet education being conducted in Honduras.

"Some people probably feel that more on-the-job, in-the-field training would have merit," a senior official said. He said that the risk would be less for such trainers if they could carry weapons, but he stressed that the administration has no desire to send them into combat situations.