Day after stifling day for two weeks local farmers have gathered on a small rise on the edge of the Honduran Air Force school at the Palmerola Base here, to gaze in mute amazement at the activity that has shattered the tranquility of this valley in central Honduras.

Where once about 100 Honduran cadets and instructors had used the tiny base, now nearly 1,000 men are swarming around its tiny runway, stacking crates of supplies and building a small tent city. Where previously only the odd training helicopter or T28 prop trainer would circle lazily in the tropical sky, the air now is rent increasingly by the whine of C130 transport planes landing in relays to disgorge cargoes of men and war materiel.

Under the gaze of the valley's inhabitants, Palmerola is being transformed into a sophisticated nerve center for the U.S. armed forces Readiness Command to conduct prolonged joint military exercises with Honduran troops that will last into next year. President Reagan has ordered the maneuvers as a warning to Honduras' southern neighbor, Nicaragua, which he has charged is providing arms for leftist rebels fighting the U.S.-backed government in El Salvador.

The joint task force's main offices have been set up in a series of air-conditioned, accordion-pleated mobile units, and giant antennas connecting the base with worldwide U.S. military communications are visible above a low canopy of scrub trees.

Nearby, U.S. soldiers in khaki tank tops sweat as they erect enclosed latrines, tents, mess quarters, shower areas and other assorted facilities for the camp that looks at the moment like a set straight out of "M*A*S*H."

U.S. military spokesmen here say that when the headquarters for the joint U.S.-Honduran military exercises are finished by the end of this month, 1,500 U.S. troops will be in residence. Their job is to coordinate, command, control and supply 3,500 other members of the U.S. Army, Navy, Marines and Air Force who will be participating in a series of military training operations around the country.

These exercises will include the building of airstrips and lengthening of port facilities, artillery training for the Honduran Army, brigade-sized field maneuvers, a marine amphibious landing on the Caribbean coast and Green Beret counterinsurgency training about 20 miles from the Nicaraguan border on a narrow strip of land considered the main infiltration route for guerrillas and arms moving north to El Salvador.

The operations here began officially Aug. 5 when the first U.S. planes began ferrying into Honduras a vanguard of men and supplies to relay to this tiny air strip. The military exercises are not scheduled to begin, however, until some time next month when all of the U.S. forces and equipment are in place. Only 800 U.S. military men have arrived in the country.

Officially labeled Ahuas Tara II--which means Big Pine II in the Miskito Indian language--the large-scale maneuvers in this impoverished Central American nation have been declared as nothing more than a "routine" operation by the Reagan administration. But coupled with the separate sea maneuvers of two different aircraft carrier task forces off the Caribbean and Pacific coasts of Nicaragua, they are viewed here as part of Washington's "big stick" policy to intimidate the Marxist-influenced Sandinista government in Nicaragua.

That interpretation, however, was not one U.S. military commanders here were willing to address. "This exercise is not more sensational than any other," insisted Col. Arnold Schlossberg, the joint task force commander, when he met recently with a group of journalists here. "We conduct exercises like these, even bigger ones, in many places of the world."

A Vietnam veteran with silver gray hair and steely eyes that stare from behind gold-rimmed aviator glasses, Schlossberg termed the exercises "a marvelous opportunity for U.S. forces because it allows us to practice deployment from the U.S. abroad and a chance to train our troops in an area and terrain they are not familiar with."

Although Schlossberg's emphasis was clearly on the benefits of the exercises to the U.S. units, he also said it would be an important experience for the Honduran armed forces, which will participate along with the U.S. units in a variety of simulated operations they have never tried.

Obviously aware of public criticism of the maneuvers, Schlossberg emphasized that Big Pine II has a "humanitarian" side. He said that between practicing war maneuvers, his troops also would conduct "people-to-people" meetings with Hondurans, U.S. medical teams would provide public health services to local residents and all efforts would be made to "establish good relationships with the Honduran people."

The colonel added that his men even would be bringing "toys for the children of Honduras and clothes, collected by charities, for the needy."

Beyond that, he said, a special well-drilling team that will come for the airfield construction will be sent out to drill water wells for potable water in neighboring communities.

For all the talk of the civic actions, however, it is the military exercises being scheduled that give Big Pine II the character of a calculated act of intimidation against Nicaragua.

Undoubtedly the most sensitive activity of Big Pine II will be the deployment next month of a team of 70 members of the 2nd Battalion of the 7th Special Forces into a narrow strip of Honduras that separates El Salvador from Nicaragua.

Based in and around the southern town of Choluteca, the Green Berets will conduct a series of counterinsurgency exercises in September and October with four separate Honduran infantry battalions in the steamy coastal plain that is considered the main infiltration route from Nicaragua to El Salvador. Engineers, meanwhile, will build an air strip in nearby San Lorenzo and instruct Honduran Army engineers on the construction of antitank traps in the one region of this hilly country where Nicaragua's newly supplied Soviet-made tanks could conceivably be used.

The other focus of the exercises will be on Honduras' northern Caribbean coast near the small port of Puerto Castilla where the United States already has set up a small military base for the training of Salvadoran and Honduran soldiers by military advisers. A team of Navy Seabees will enlarge the local airstrip near the port and extend the port's quay to provide for the docking of larger ships. Nearby in the countryside the 3rd Battalion of the 319th Field Artillery will stage artillery fire and control practice with 150mm howitzers, demonstrating their use to Honduran troops whose biggest field weapon to date has been a mortar.

In November, about 2,000 combat troops from the 28th Marine Amphibious unit out of Camp Lejeune, N.C., will stage a landing on a beach near the port and hold seven to 10 days of maneuvers on land with Honduran troops before sailing home. The climax of the exercises is to be a Honduran brigade-sized field maneuver using four or more infantry companies with U.S. logistic and air support. U.S. military spokesmen here remain imprecise about when that final exercise will be held and say only that it will be after the first of the year, possibly as late as March.