TEGUCIGALPA, HONDURAS -- A network of Sandinista spies and saboteurs inside the most sensitive Nicaraguan rebel bases here has seriously damaged the insurgents' air resupply operations and embarrassed both them and their U.S. backers, according to rebel and diplomatic sources here.

The Nicaraguan rebels, who are known as counterrevolutionaries or contras, blame the spy and sabotage network for the crash of two resupply planes in Honduras and the mysterious deaths of several wounded rebel combatants.

The network of about a dozen Sandinista infiltrators in the rebels' Honduran operations was discovered in April by a special contra counterintelligence unit, rebel officials said. Among the suspected Sandinista spies nabbed in the sweep, they said, was the driver of Aristides Sanchez, a senior rebel leader who lives here. Sanchez is the logistics chief of the largest contra army, the Nicaraguan Democratic Force, and a director of a new rebel umbrella organization called the Nicaraguan Resistance.

According to a contra official, at least one Sandinista infiltrator was a paramedic who allegedly killed a wounded contra with a lethal injection. Others are said to have operated with contra field units and inside the rebel military headquarters at Yamales near the Nicaraguan border.

A contra official declined to specify what had become of the captured spies.

Discovery of the network has revealed valuable information about the plans and methods of Sandinista intelligence, including specific targets for assassination and sabotage, the official said. He said some of the Sandinista agents had been trained by Cubans.

An investigation into the affair is continuing, the official said. He said the ringleader of a Sandinista cell that sabotaged the contra planes, a talented young mechanic working at the Aguacate air base in central Honduras, had confessed and implicated other cell members, who were also arrested.

Aguacate, the main air base of the Nicaraguan Democratic Force, is the takeoff point for many of the flights that supply contra units inside Nicaragua. The Sandinistas charged that a twin-engine Beechcraft Baron plane, shot down last week after allegedly rocketing military positions and dropping leaflets inside Nicaragua, had flown from Aguacate.

According to a western diplomat, contra officials here initially boasted about breaking up the sabotage ring at Aguacate, then abruptly stopped "when they realized how embarrassing it was." Another diplomat, who closely monitors contra operations, acknowledged that spies had been captured, but questioned the rebels' assertions that they had caused the two plane crashes. He suggested that the contras might be claiming sabotage to cover up their own mechanical faults.

Some contra officials, on the other hand, have blamed the security lapse at Aguacate on the CIA, which oversees the contra air resupply operation.

"The Americans get nervous about this," one contra official said of the spy network. "It makes them look clumsy."

According to contra officials, the Sandinista mechanics at Aguacate last September sabotaged a contra DC3 supply plane, which had to crash-land near the town of Teupasenti in south central Honduras. Earlier this year, a contra DC6 crashed on takeoff at Aguacate when its nose wheel collapsed as a result of suspected sabotage, rebel sources said. No one was seriously injured in either crash, they said, but both aircraft were wrecked.

A contra official said the mechanics tried to sabotage the fuel system of another plane, a C47, but this was discovered in time.

Another contra source said the mechanics passed intelligence information to Sandinista agents in the town of Catacamas near Aguacate and were sometimes visited by Nicaraguans they described as relatives, who apparently were Sandinista spies. The driver of rebel leader Sanchez also was frequently visited by relatives, the source said.

According to another version of the Sandinistas' activities at Aguacate, the cell used a secret radio transmitter to send intelligence data to Nicaragua for more than three years without detection.

One contra source indicated that the crash of the two planes reduced the rebels' air resupply fleet by a third. He said the contras now supply their forces with two planes based at Aguacate and two flying from Swan Island off the Honduran Caribbean coast.

"We have only one DC6 left," another rebel official lamented. He argued that more of these planes, which he said can carry 20,000 pounds of cargo, compared to 4,000 pounds for a C47, are urgently needed to help resupply the 10,000 fighters who the contras say are currently operating inside Nicaragua. He estimated that each contra regional command, made up of 800 to 1,200 guerrillas, requires 15,000 to 20,000 pounds of supplies a month.

"Our capacity of resupply is not sufficient," a rebel commander said in an interview. "Right now it's like trying to put out a forest fire by throwing glasses of water on it. We don't have big enough planes."

According to the Nicaraguan Embassy here, however, the contras have at least 15 aircraft, including helicopters, that operate from Aguacate, Swan Island, the Salvadoran military air base of Ilopango and Florida.

The Sandinistas have put a great deal of effort into building an intelligence network and infiltrating agents into contra ranks. It is generally assumed that Sandinista spies operate widely in Honduras and Costa Rica.Special correspondent Wilson Ring also contributed to this article.