The CIA plane that crashed yesterday went down near the peak on the San Salvador Volcano three miles from the edge of the capital, national guardsmen protecting a communications facility here said today.

A U.S. Embassy official had said yesterday that the plane crashed on another mountain, Guazapa Volcano, 15 miles north of he capital. Four U.S. citizens working for the CIA died in the crash, according to the U.S. government.

The plane's crash so close to San Salvador, and on the side of the peak that faces the capital, appeared to raise questions about the nature of its mission and the origin of the flight.

U.S. officials in Washington said yesterday that the spy plane had been on a mission near the Salvadoran border collecting information on left-wing insurgents' activities and seeking evidence that the rebels receive supplies from Nicaragua. Intelligence sources in Washington said that such flights originate in Palmerola Air Base in Honduras. Today, officials in Washington said the plane had been following another aircraft, believed to be on a rebel supply mission.

But the plane crashed in the center of El Salvador in territory that is firmly under government control and is not known to be on the flight path of rebel supply planes, which are believed to operate far to the east and north.

Officials in Washington emphasized that weather was so poor in the area that it could have affected the positions of both planes. Military observers here suggested that the American flight might have originated at Ilopango Air Base in San Salvador. A U.S. official here expressed surprise when told that intelligence sources had indicated that the flight had originated in Honduras.

"We're not saying that. I hadn't heard that," the official said.

The U.S. official who had said yesterday that the flight had crashed on Guazapa backed off from that statement today. "It was in the vicinity of San Salvador. I thought it was on Guazapa. That was my understanding," the official, who insisted on remaining anonymous, said today.

The Salvadoran Armed Forces maintain an observation post on the top of Guazapa, but the guerrillas usually hold the volcano's slopes. The Salvadoran Air Force regularly bombs that volcano's slopes, and the Army routinely marches through the area hunting the insurgents.

Ilopango has been used in the past for U.S.-backed covert operations, according to published reports. In particular, planes flying out of Ilopango have delivered supplies to Nicaraguan antigovernment rebels based in Costa Rica.

The plane's crash provided the first evidence that CIA flights -- as distinct from military aircraft -- are gathering intelligence over El Salvador. U.S. Army surveillance planes based in Honduras and Panama are known to collect data on the Salvadoran rebels.

The embassy said the plane crashed during a violent storm before dawn yesterday. The left-wing rebels' clandestine Radio Venceremos said today that the plane had been "downed" but provided no details about where or how. It said that the plane had flown over the northeastern province of Morazan, 80 miles from San Salvador, to help the Salvadoran Army during an offensive against a rebel stronghold there.

Journalists acting on a tip from a Salvadoran source drove to the top of El Picacho -- the highest peak on the San Salvador Volcano, at an altitude of 6,370 feet -- to search for the plane's wreckage. A Salvadoran Air Force officer at the communications facility here refused to allow the search.

"The order comes from the general staff," the officer, who would identify himself only as Lt. Villeda, said. Villeda said that he had arrived only yesterday, and a national guardsman said that Salvadoran Air Force officers and soldiers had come yesterday, said that they were hunting for an unidentified "objective," and refused to allow the guardsmen near the plane's wreckage.

But three guardsmen said that they knew where the plane had crashed, and they and villagers on the volcano's slopes said that they had seen a small plane and several helicopters flying around the peak yesterday. One guardsman said that a helicopter had been seen lifting stretchers at the end of ropes.