President Reagan yesterday acknowledged U.S. support of anti-government guerrillas in Nicaragua but said his administration was "complying fully" with a congressional prohibition on activities aimed at overthrowing Nicaragua's leftist Sandinista regime.

"Anything we're doing in that area is simply trying to interdict the supply lines which are supplying the leftist guerrillas in El Salvador," the president said at a brief news conference. "But the picture today is that Nicaragua, with its protests that somehow someone is trying to overthrow them, is, as a revolutionary government, trying to overthrow the government of . . . El Salvador . . . . "

A high administration official said later that "part of the interdiction" was the use of sophisticated Airborne Warning and Control System (AWACS) aircraft to spy on air traffic in and out of Nicaragua. The planes, based at Tinker Air Force Base, Okla., are refueled in midair over Mexico and are blanketing Nicaragua with radar surveillance from the safety of international waters in the Pacific, officials said.

While Reagan publicly insisted in the White House briefing room that his administration is obeying the law in Central America, Secretary of State George P. Shultz and national security adviser William P. Clark were making the same argument in the Capitol to Rep. Edward P. Boland (D-Mass.), chairman of the House Permanent Select Committee on Intelligence.

Boland is the author of an amendment bearing his name that prohibits U.S. assistance "for the purpose" of overthrowing the Nicaraguan government or provoking military conflict between Nicaragua and neighboring Honduras.

The 35-minute meeting was described by administration officials as "a good, friendly consultation on our policy in El Salvador and Nicaragua" in which Boland did not assert that the Reagan government is violating the law. They described Boland as "cordial and non-committal, as we expected."

But a congressional source said Boland "expressed a very serious amount of concern" among committee members about whether the administration was complying with the law. "I don't think it was a meeting to change anyone's position," the source said.

Each side listened carefully to the opposing concerns and agreed at the end of the meeting that Shultz would return Wednesday to testify before the full committee in closed session. Clark does not plan to testify, in keeping with what the White House described as a long tradition.

Reagan made his comments on Central America at a news conference called to celebrate the Senate confirmation of Kenneth Adelman as director of the Arms Control and Disarmament Agency. But reporters ignored that announcement and all their questions except one were about administration policy in Central America.

The president, after first saying he couldn't say anything except that the administration was "complying with the law," launched a vigorous defense of his policy and an attack on the "completely Marxist" government of Nicaragua.

"We are not doing anything to try and overthrow the Nicaraguan government," Reagan said. " . . . Nicaragua today has created the biggest military force in all of Central America and large parts of South America--an army of some 25,000 backed by a milita of 50,000, armed with Soviet weapons that consist of heavy-duty tanks, an air force, helicopter gun ships, fighter planes, bombers and so forth . . . ."

Reagan said that Nicarauguan armed force was opposed by a few thousand Miskito Indians and guerrillas and added, "I don't think it's reasonable to assume that that kind of a force could nurse any ambitions that they they can overthrow that government with that great military force."

In previous intelligence and State Department reports, the administration has never asserted that the Nicaraguans possess an air force of any significance. The air force is mainly a few old trainers and civilian propeller planes, although Nicaragua has received modern artillery and heavy tanks from Cuba and the Soviet Union, according to these reports.

Reagan attempted to turn around criticism that the United States is supporting efforts to overthrow the leftist Nicaraguan government by insisting Nicaragua is trying to overthrow the elected government of El Salvador by supplying arms to leftist insurgents. The president hinted that he would take action to prevent this if permitted, but said "what I might personally wish or what our government might wish still would not justify us violating the law of the land."

White House counsellor Edwin Meese III also reflected administration unhappiness with the Boland amendment at a breakfast meeting with reporters. He said, "It is the responsibility of the president to conduct foreign policy; limitations on that by the Congress are improper as far as I'm concerned."

The administration's point man on Central American policy, Thomas O. Enders, deputy secretary of state for inter-American affairs, returned to Capitol Hill yesterday to brief the House Foreign Affairs Committee and wound up in a heated exchange with Rep. Robert Torricelli (D-N.J.), who was in a fact-finding group that returned this week from Nicaragua.

Torricelli accused Enders, who also attended a portion of the meeting with Clark, Shultz and Boland, of making "inflammatory" charges that the Nicaraguans were prepared to accept Soviet missiles on their soil. Torricelli said Enders was using scare tactics to justify a hardline policy toward Nicaragua. Torricelli said that Nicaraguan officials told him explicitly that they "have no intention of basing offensive Soviet weapons in Nicaragua."

"Recognize what this Nicaraguan missile crisis is all about," Torricelli said. "They are searching for facts to justify a policy."

Enders defended himself by saying he was simply repeating what had been reported in news accounts from Managua based on remarks by the Nicaraguan defense minister. After the hearing, Enders said, "We were just quoting the Nicaraguan defense minister. Mr. Torricelli has received a denial. As far as we can tell, they have not denied it in public, but it would be very welcome."

Meanwhile, the State Department issued a response to Torricelli's claim on Wednesday that the U.S. ambassador to Honduras, John D. Negroponte, had called the Boland amendment a "legal triviality." A department spokesman said Negroponte "flatly denied" making the statement.

Administration officials said last night that former senator Richard Stone (D-Fla.) would be designated "legislative coordinator" in Congress for the administration's Central America policy and probably would take a trip to the region next week.