Leftist guerrillas claim to have shot down a helicopter today carrying the Salvadoran deputy defense minister and the field commander of government forces that are locked in some of the hardest combat of the war.

There was no immediate independent confirmation of the report, but Deputy Defense Minister Francisco Adolfo Castillo had said to reporters earlier in the day and to other sources in the capital last night that he intended to visit the front in northern Morazan department this afternoon.

The clandestine guerrillla Radio Venceremos said three helicopters overflew the combat zone near the villages of Perquin, which the guerrillas took 12 days ago, and San Fernando, which they have had under siege for about the same amount of time.

The broadcast said that one of the helicopters was shot down and that both Castillo and Sixth Brigade Commander Col. Salvador Beltran Luna were in it.

If Castillo and Beltran Luna are dead they would be by far the most senior officers killed in the two-year-old civil war here. A lieutenant colonel was shot in combat in March.

But it was not clear from the broadcast whether the guerrillas were claiming to have killed the two officers. On several previous occasions the insurgents have forced down government helicopters, including some of the 20 UH1H "Hueys" supplied by the United States, but the government has been able to defend both the machines and their crews until they could be rescued.

Castillo, a quiet, professional officer who apparently steered clear of much of the political intrigue that plagues the Salvadoran armed forces, attended a ceremony in the eastern port city of La Union this morning to hand out land titles to peasants as part of the Army-backed agrarian reform program.

From there, he told reporters, he was planning to go to Morazan, where an estimated 3,000 troops that have been pitted against well-entrenched guerrillas from the People's Revolutionary Army faction of the insurgent front.

In the departmental capital of San Francisco Gotera today, soldiers and townspeople talked of fierce fighting to the north, and some young recruits who had been involved told of perhaps two partial companies of about 80 men each who have been "lost."