Antigovernment guerrillas killed 22 persons in an ambush of a truck carrying coffee pickers yesterday, the bloodiest of a series of recent attacks aimed at disrupting the harvest, government officials and survivors of the raid said today.

In a separate incident, government forces ambushed and "completely broke up" a guerrilla force, killing 35 rebels, including several "important" leaders, the Interior Ministry reported.

The two attacks -- both with relatively high casualty tolls -- appeared to signal the start of a widely expected intensification of the war in northern Nicaragua as the guerrillas try to block the economically vital coffee harvest.

Thousands of guerrillas of the Nicaraguan Democratic Force, based in isolated mountains near the Honduran border or in central provinces, have begun in recent weeks to strike coffee farms or vehicles carrying pickers. The rebels, who were organized and previously were financed by the CIA, are battling to overthrow Nicaragua's left-wing Sandinista government.

About 150 guerrillas fired machine guns and grenade launchers at a truck carrying 31 persons yesterday at 7:45 a.m. near the hamlet of El Pericon, in the northern province of Madriz, according to government officials here and three wounded survivors interviewed at a hospital in La Trinidad.

About half of the pickers carried Soviet-made AK47 automatic rifles because of the danger of attack, but the guerrillas killed armed and unarmed pickers alike, the survivors said. The survivors said rebels killed several wounded persons lying on the ground by shooting them or stabbing them with bayonets, and they set the truck afire with at least three wounded persons inside the vehicle, including a boy under 10 years old.

"I heard the people in the truck crying out when they set it afire," Santos Briones, 15, said as he lay in bed with a bullet in his left foot. He was about six feet from the truck at the time, pretending to be dead, he said.

"I crawled under a dead comrade and smeared my face and chest with blood," Briones said. His mother, whose son Jorge also was wounded in the raid, was standing at the foot of the bed and interrupted the interview to say: "All of the contras' counterrevolutionaries' weapons were made in the United States. Please tell the American people in your newspaper to leave us in peace."

Nearly all of the pickers were employes of the state telecommunications company. They, like many government employes, have been recruited to pick coffee during the harvest period from late November through February. Favorable weather has yielded a good crop on the coffee bushes, but there is a severe shortage of pickers because people are afraid to work in areas where they might be attacked.

Only a couple of the armed pickers were able to fire back at the rebels, as most apparently were killed or wounded in the initial attack, the survivors said. Six pickers were wounded, while the rebels carried away several wounded of their own, the survivors said.

In the other incident, special forces of the Interior Ministry attacked a guerrilla force in the Santa Rosa hamlet near La Trinidad in Esteli province yesterday, according to a ministry communique in today's newspapers. The Interior Ministry has its own military forces, which apparently are used as elite shock troops against the guerrillas in operations separate from those of the regular Army.

The ministry said its troops killed the rebel force's second in command, identified by his code name "Valiente," and other leaders of the force.

The communique also said that the General Office of State Security, which is part of the Interior Ministry, had located the guerrilla force by capturing and questioning two guerrilla fighters on Nov. 27.

The ministry reported only one casualty of its own, a second lieutenant who was decorated posthumously for his courage.