The U.S. military is planning next month to stage its largest exercise in Honduras, sending more than 6,600 troops to the Central American nation to practice an amphibious landing with support from attack helicopters and guided missile ships, Pentagon officials said yesterday.

The exercise, called Universal Trek '85, is to last two weeks and would be the fifth major maneuver conducted by the two nations since 1983. Past exercises have lasted longer, but none involved troops.

Another maneuver, Big Pine 3, a three-month mission in which tanks were sent to Honduras for the first time and as many as 4,500 troops were deployed at its peak, will be operating in another part of the country when Universal Trek '85 is to take place nearby on the northern coast April 23.

Reagan administration officials have said the exercises are aimed at shoring up the Honduran military and intimidating the leftist Sandinista government of neighboring Nicaragua, which U.S. officials accuse of having designs on Honduras. The exercises coincide with an administration push in Congress for release of $14 million in aid to rebels opposing the leftist Nicaraguan government.

Honduras agreed to the maneuvers despite earlier reports that some of its military officers have been eager to scale back the U.S. military presence unless Washington guarantees more aid and a security pact. About 1,300 U.S. troops are stationed in Honduras on a regular basis.

Universal Trek '85 is to involve an amphibious landing far from the Nicaraguan border on the coast near Puerto Castilla, sending 750 Marines ashore as Cobra attack helicopters and ships provide cover, according to officials. An air assault task force from the 101st Airborne Division is to join the Marines ashore and move into the interior, the officials said. In all, 3,000 U.S. troops are to participate in the landing, supported offshore by a guided-missile cruiser, destroyer and frigate.

The exercise is scheduled April 12-27 and is to involve 1,000 soldiers, 2,200 Marines, 3,250 Navy personnel and a joint headquarters staff of 180, the official said.

Between 5,000 and 5,500 U.S. troops participated in the previously largest Honduran exercise, Big Pine 2, which lasted from August 1983 to February 1984 and included an amphibious landing.

When Pentagon spokesman Michael I. Burch announced Big Pine 3 in January, he said its peak force of 4,500 troops would comprise the largest exercise of the year in Honduras. It is unclear why the administration decided to send yet a larger force next month.

Honduran leaders have expressed reluctance about their country becoming the center of U.S. efforts against Nicaragua and insurgents in neighboring El Salvador. They have staked out independent policies while demanding more U.S. economic and military aid and written defense commitments.