The Nicaraguan Army's incursion into southern Honduras this week reflects the leftist Sandinista government's growing confidence that its troops have gained a decisive upper hand against U.S.-backed rebels, as well as decreasing concern about the debate in Washington over contra aid.

Sandinista military leaders claim to have dealt a "strategic defeat" to what they term the counterrevolutionaries in the last six months. "The Sandinistas believe they are close to doing irreversible damage to the contras," said a well-placed diplomat in Managua in a recent interview. As the weeks multiply in which the contras are unable to mount a significant attack against Sandinista positions inside Nicaragua, the Nicaraguan government is more inclined to pursue its own military timetable, regardless of the results in Congress.

Troops from three Sandinista battalions, now estimated to have numbered about 800 soldiers, moved 10 miles into Honduran territory in an attempt to annihilate a contra training camp and a field hospital, according to intelligence sources in Honduras. The Nicaraguan troops, who apparently were guided by faulty intelligence about the strength of contra forces near the border, were said to be retreating into Nicaragua yesterday after being repelled by contra guerrillas.

In part, the Sandinista government appears surprised by the hubbub surrounding the incursion, since its troops have ventured over the ill-marked, mountainous border repeatedly in the past in pursuit of contra fighters whose camps are in southern Honduras. In a statement released yesterday in Managua, the Nicaraguan Defense Ministry admitted that it had destroyed rebel base camps, but did not say explicitly that the camps were located in Honduras.

Last May, the Sandinista Army launched an attack on Las Vegas, then the contras' main base camp, five miles inside Honduras. Soon the contras were obliged by edgy Honduran military officials to break down their operations into smaller, less conspicuous camps along the border. The Honduran government generally has turned a blind eye to the border violations because it has been reluctant to admit that the contras are staging their warfare from Honduras.

Recent statements by Sandinista leaders also indicate that they have concluded that there is little they can do, positively or negatively, to influence the outcome in Congress concerning the contra aid. Sandinista analysts believe the House of Representatives eventually will approve some amount of military aid for the rebels. "They have given up any hope that the Democrats will put an end to the contras' war," said William LeoGrande, a political science professor at American University who specializes in Central America.

Instead, U.S. officials suggest, the Sandinistas saw this period between congressional votes as an opportunity to pressure the Honduran government and to strike a demoralizing blow against the contras while they were resting in Honduras.

"I think they made a decision to do as much damage as they could to the contras and also raise the heat on the Hondurans," said a U.S. official here.

On Wednesday, the Nicaraguan Embassy here released a statement calling for the formation of an international commission to patrol the border between Honduras and Nicaragua, similar to one being formed for Nicaragua's southern border with Costa Rica under the auspices of the Contadora peace group.

A State Department official speculated that the Sandinistas viewed the incursion as a show of military muscle to impress the Hondurans with the need for a bilateral agreement on the border. "They did what the Sandinistas do best: create a problem and then propose a solution that fits neatly into their plans," the official said.

The Sandinistas believe that the Honduran government led by President Jose Azcona is in a conciliatory mood, according to Latin and other western diplomats in the region. The diplomats said that during Azcona's inauguration in late January, the new president told Nicaraguan Vice President Sergio Ramirez that Honduras would like to reach a border accord with Nicaragua but is constrained from doing so because of its U.S. commitments.

Throughout this year's debate over contra aid, the Sandinistas have shown little interest in the ebb and flow in Congress. Earlier this month, Nicaraguan President Daniel Ortega spent a week vacationing in Cuba, and comments by other senior Nicaraguan officials have been few and relatively muted.