Washington — President Reagan's secret aid plans for Nicaraguan guerrillas have been slowed by congressional opposition. It is now possible that within weeks, the Congress will blow those plans completely out of the water.
The United States Central Intelligence Agency (CIA) is reported to have suspended its mining of Nicaraguan harbors. Given the uproar in the Congress, it now seems unlikely to resume them.
Congressional specialists say that even if Congress agrees to continue funding CIA-backed guerrillas fighting in Nicaragua, it is likely to place tighter restrictions on how the money is used. Congress is also expected to demand fuller reporting to congressional intelligence committees on the supposedly secret operations.
But with Congress in recess, the legislative process is fraught with uncertainties. Perhaps the only certainty is that some form of Senate-House conference on covert aid will take place.
On April 5, the Senate approved an additional $21 million for the Nicaraguan rebels. But the House is now in less of a mood to compromise on the issue. The Democrat-dominated House has voted twice along party lines to suspend aid to the Nicaraguan rebels. Also voting along party lines, the House Intelligence Committee on April 11 rejected President Reagan's request for additional aid.
The most-heavily publicized criticisms of the administration's handling of the CIA-sponsored mining operations have come from the leading Republican and leading Democrat on the Senate Select Committee on Intelligence. Both have charged that they were not fully informed of the operations, as required by law. On Sunday, Sen. Daniel Patrick Moynihan, a New York Democrat, resigned in protest from his position as vice-chairman of the committee.
The Republican committee chairman, Sen. Barry Goldwater of Arizona, in a now famous ''Dear Bill'' letter to CIA Director William J. Casey, denounced the mining of harbors as ''an act violating international law'' and ''an act of war.'' Senator Goldwater told Mr. Casey that his guess was that the House of Representatives would defeat the administration's supplemental aid bill and that the Senate committee ''will not be in any position to put up much of an argument after we were not given the information we were entitled to receive.''
Congressional specialists on the House side tend to support Goldwater's statement. As one aide to a key Democrat put it, ''The House will simply not go along with the Senate on this.''
Where the disclosure of the controversial mining operations appears to have done the most damage to the administration is among senators and congressmen who only reluctantly went along with funding for the Nicaraguan rebels, or ''contras ,'' as they are often called. As a congressional aide put it, ''Some people are going to start saying, 'Wait a minute. This far, and no farther.' ''
Among those who had provided backing for ''limited'' covert operations was Sen. David F. Durenberger, a Minnesota Republican serving on the Senate Intelligence Committee. More than a year ago, Senator Durenberger played a key role in trying to get the administration to move away from what looked like an ''open ended'' Nicaragua program to something more carefully defined. Durenberger thought he had assurances on that issue. He also thought the administration was pledged to consult at least once a month with the committee on the Nicaragua program, which it apparently did not do.
According to Senate staff members, a more than 80-page report presented by the CIA to Senate committee members in March concerning Nicaragua programs contained only a short reference to mining, which was ''buried'' in the report in such a way as to make the mining seem unimportant. There was no indication, staff members say, that the CIA was running a ''mother ship'' and supervising the mining, as now appears evident.
Congressional objections to the mining have been for the most part twofold:
1. The mines are ''indiscriminate'' - they do not single out Soviet arms-supply ships. They have damaged not only a Soviet vessel but also ships from Western nations.
2. The mining represents more of an ''Americanization'' of the fighting in Nicaragua, with a more direct CIA role.
''I think the Senate could live with a program supporting Nicaraguan frogmen who are attaching limpet mines to arms-carrying ships,'' said one Senate staff specialist.
As best one can gather from congressional sources, meanwhile, CIA Director Casey's attitude toward the mining blowup in Congress can be summed up by the words: ''What's all the fuss about?''
Casey reportedly described the mining to senators last week as a nonvital part of the CIA program against Nicaragua.
In Casey's view, the mining should be regarded as a matter of harassment - one more means of deterring Nicaragua's Sandinistas from ''exporting revolution'' and arms to El Salvador and other Central American nations. As he explained it, the mines are ''nonlethal.'' They are designed not to sink ships, but to frighten others away from Nicaragua's harbors.
What Casey and other administration officials appear to have underestimated was the degree to which the Congress is leary of more direct American involvement in the Central America fighting - an outgrowth in part perhaps of the so-called Vietnam syndrome.
But interestingly, the loss of congressional trust in Casey does not necessarily extend to the CIA as a whole. Many senators and congressmen are apparently convinced the CIA is operating strictly within its orders from the administration. The CIA is not a ''rogue elephant,'' they say.