Security forces killed 77 leftist guerrillas Friday in two separate attacks in the Andes Mountains and the jungle, the government said. It was the heaviest day of fighting in Peru's nine-year insurgency.

Six soldiers and three university students also were killed, officials said.Also Friday, the officials said more than 6,000 people were detained in Lima in massive sweeps by police seeking the killers of leftist congressman Eriberto Arroyo, who was slain Thursday.

At dawn, troops spotted a column of leftist guerrillas in uniforms near Molinos, a tiny village 35 miles north of Huancayo, the government said in a communique.

In fighting that followed, 62 leftist guerrillas and six soldiers were killed and 23 soldiers were wounded, it said.

President Alan Garcia said in a brief radio statement that the rebels were from the Tupac Amaru Revolutionary Movement, which endorses a Cuba styled Marxism and has been active since 1984.