TEGUCIGALPA, HONDURAS -- Sandinista troops have blown up a key airstrip used by Nicaraguan rebels on the Honduran-Nicaraguan border in heavy fighting that ended earlier this month, according to rebel sources.

After more than three weeks of fighting in which the site on the Honduran side of the border changed hands three times, the sources said, the Sandinistas blew up the grassy strip with 17 explosive charges, then withdrew across the Coco River into Nicaraguan territory. The airstrip, located on high ground above the northern bank of the Coco at the mouth of the Bocay River, had been used to drop supplies to rebels in the area and ferry visitors, including journalists, to a jumping-off point for trips into Nicaragua with rebel forces.

Accounts of the battle for the airstrip suggested that the fighting in the Bocay area went on longer than the Sandinistas said it did, and that the rebels' bases in the zone were more important to them than they later claimed. The varying versions of the Bocay fighting also illustrated the different interpretations that the two sides often place on the same event, complicating assessments of the war.

The Nicaraguan Embassy here said the Sandinista assault on the Bocay area, which began May 10 and lasted three days, represented a further "strategic defeat" for the rebels and denied them a key propaganda tool. Ambassador Danilo Abud Vivas said Sandinista forces continued to occupy the uninhabited area of dense jungle in northern Nicaragua's Jinotega province to ensure that the rebels, who are known as counterrevolutionaries or contras, could not return.

According to contra officials, however, the operation has been costly for the Sandinistas, who deployed 3,000 troops, backed by artillery and helicopter gunships, in the assault on the rebel stronghold, 180 miles north of Managua at the confluence of the Bocay and Amaka rivers. The contras said the Sandinistas had been drawn into a strategically useless zone, far from resupply centers, that they will now have difficulty leaving.

"The Sandinistas felt we were threatening their portrait of us as only making forays across the border," a contra official said. "Now we have outmaneuvered them tactically and put them in a difficult strategic position. If they withdraw their forces, it will be their Waterloo. If they stay, it will be at terrible cost."

"Apparently the Sandinistas reason with the mind of a bull," he added. "After this operation we are more optimistic about our chances."

Contra officials maintained that in pursuing a guerrilla strategy, they do not try to control fixed positions. They said the bulk of their forces in the Bocay area made a "tactical retreat" and dispersed to the east and west when the Sandinistas launched their attack. They said the contra forces that actually took part in the battle numbered fewer than 200 fighters and that their casualties were light.

Contra sources said that in three weeks of fighting that started May 10, they suffered three killed and 30 wounded, six of them seriously. Four other contras were reported missing in action. A rebel commander who took part in the fighting said two contras were killed and nine wounded on the first day of the battle.

In the course of the fighting, the contras claimed to have shot down two Soviet-supplied Mi17 Sandinista helicopters, one of them with a U.S.-made Redeye heat-seeking missile, and to have killed 50 Sandinista troops.

According to the Nicaraguan defense minister, Gen. Humberto Ortega, Sandinista troops found the bodies of 32 contras and "various supplies" in the jungle after the assault, which he said routed the rebels from Nicaraguan territory in 36 hours.

In a May 13 news conference, Ortega put Sandinista casualties at eight dead and 63 wounded since April 25. He denied that Sandinista troops had crossed into Honduras during the three-day operation. In a subsequent visit to the battle area in Sandinista helicopters, journalists were shown the bodies of two contras and several abandoned huts as evidence of the Sandinista victory.

It was not possible to confirm either version of the Bocay battle independently.

A European diplomat said that after publicly boasting about their Bocay "forward resupply base" and saying they would defend it, the contras hastily abandoned the area in a military and psychological defeat. He said that about 800 fighters had fled across the border into Honduras in the face of a much stronger Sandinista offensive than the contras had expected.

"The edge seems to have gone off their morale," the diplomat said. "When the going got tough, the contras got going -- backwards."

On the other hand, an American free-lance cameraman who traveled with the contras earlier this month on the Honduran side of the Coco River reported that the rebels had a Sandinista unit pinned down on the embattled airstrip. He brought back footage showing the bodies of Sandinista soldiers floating down the river from the site.

He added that the Sandinistas subsequently withdrew across the river into Nicaragua about June 8 after blowing up the airstrip.

Contra sources asserted that the Sandinistas' heavy commitment to the Bocay assault allowed contra units to attack targets more easily elsewhere. A contra official cited a recent attack on what he described as a Sandinista Army garrison in the rural community of Abisinia about 120 miles northeast of Managua. He said a unit of the contras' Salvador Perez Regional Command operating in Jinotega province overran the headquarters of the Sandinistas' 400-member 3643 Battalion at Abisinia.

The Sandinistas said Abisinia was only lightly defended by 18 local militiamen when the contras launched a predawn attack with rocket and mortar fire June 2. The attack reportedly destroyed private homes and government buildings, leaving a dozen people dead.