MANAGUA, Nicaragua — U.S.-backed rebels attacked a strategic town in northern Nicaragua early Thursday, and 22 people were reported killed in three hours of fighting. The rebels said they

seized control of San Jose de Bocay, 92 miles northeast of Managua, and blew up the town’s army garrison before retreating. The Sandinista army denied the claim. In any case, rebel spokesmen

said the assault signaled a shift toward military targets after months of growing rebel sabotage attacks on electric power installations, roads and other civilian objectives. The town is

the main staging center for the Sandinista army in north-central Nicaragua. It lies in a valley used as the rebels’ principal infiltration route from Honduras. The Nicaraguan Defense

militiamen and 11 civilians. Bosco Matamoros, a Nicaraguan Resistance spokesman, said in a telephone interview from Honduras that four rebel task forces--about 500 men--entered the town,

damaged a helicopter landing strip and destroyed artillery and anti-aircraft weapons at the garrison. He said the rebels attacked a militia post at a farming cooperative near the town,

seizing mortars and automatic weapons. The rebel spokesman gave no casualty report. “This is a very important defeat for the Sandinistas because it diminishes their ability to operate in the

Bocay area,” Matamoros said. “It also means we are entering a new stage of the military struggle. Now we are going to start attacking more important military and strategic targets.” But the

Defense Ministry said the heaviest fighting occurred about a mile outside the town and “no damage to military installations or objectives was reported.” The attack came as the Sandinistas

prepared to celebrate their takeover of Nicaragua eight years ago Sunday in a guerrilla war that toppled President Anastasio Somoza. It appeared aimed at convincing the U.S. Congress that

the contras are an improved fighting force that deserves continued military aid in their five-year-old war. The Reagan Administration is preparing to ask Congress for $105 million in rebel

assistance for next year. At least 9,000 rebels have entered Nicaragua since Congress voted them $100 million in aid late last year. They have spread through the central and eastern parts of

the country and inflicted growing casualties on Sandinista soldiers and civilians but have yet to seize and hold a single town. Marta Sacasa, a rebel spokeswoman in Miami, said the raiding

force did not intend to hold San Jose de Bocay but claimed that by penetrating the town, the rebels had shown their support among its people. “Our objective is to demonstrate our presence,”

she said in a telephone interview. “Our tactic is to wear down the enemy and lower their morale.” Times staff writer Doyle McManus, in Washington, contributed to this story. MORE TO READ