New York Times News Service

SANTIAGO,Chile--U.S. weapons experts have accused Cuba of providing the arms found hidden in several caches in Chile recently. The experts say the amount of weapons was too large for Chilean guerrillas to have acquired on their own.

In a summary of a study made available to reporters by Reagan administration officials recently, the experts said the weapons appeared to be part of "sophisticated plans for a protracted conflict, rather than for a series of quick, hit-and-run operations designed to harass" Chilean government forces.

The unidentified experts who prepared the study said about 70 tons of munitions, including more than 3,300 American-made M-16 rifles and more than two million rounds of ammunition, was the largest clandestine leftist arsenal ever found in this hemisphere.

The arms, much of which are now stacked in a vast storeroom at the century-old War Arsenals complex in Santiago, were found buried at 10 sites from early August through early September. Most of the places were around the southern edge of the Atacama Desert, about 400 miles north of Santiago.

Robert S. Gelbard, deputy assistant secretary of state for South America, said in a telephone interview that the United States considered the discovery of the arms a sign of a "major threat to the hemisphere." He said American officials intended to raise the issue with the Soviet government.

"We feel very strongly about this," he said. "We know it is Cuba who did it, and we assume the Soviet Union is behind it."

Gelbard said the United States intended to prevent Chile from becoming "the site of an East-West confrontation."