President Reagan's senior advisers have decided to move ahead next month with a major effort to win from Congress $14 million in covert aid for the rebels fighting the government of Nicaragua, rather than seek alternative ways to help the "contras," White House officials said yesterday.

The officials said there was general agreement after a meeting on legislative strategy that Reagan should not now turn to other methods of helping the rebels, such as using a third country or transforming the aid into open assistance.

Those options could arise again, one aide said, but White House officials have decided to devote their attention to a major political offensive on behalf of the contras next month, after Congress votes on the MX missile, possibly including a nationally televised speech by the president.

A senior White House official acknowledged that Reagan is now 50 to 60 votes short in the House for his proposal to restart aid to the contras, which was terminated last year.

"That may be true as of this moment," the official said, "but we haven't put a full-court press on yet. We're working now on the MX. Give us time. If they're going to vote at the end of April, you don't want to peak at the end of March."

The White House can determine the approximate timing of the vote on aid to the contras by when it submits a report to Congress.

There have been suggestions in recent weeks that Reagan might seek to aid the contras through indirect means, avoiding Congress. But the senior official predicted that the president eventually would prevail on Capitol Hill rather than turn to other sources of help.

"I'm not talking third parties, I'm not talking from some secret slush fund or anything of that nature," the official said. "I'm talking through the Congress." Reagan will seek a vote after the Easter congressional recess, he said.