MANILA, Philippines (AP) _ The army today deployed reinforcements in mountains north of Manila to halt about 300 Communist rebels believed fleeing toward the capital, the government-run television reported.

Sporadic clashes continued Tuesday night and early today, the government- run Philippines News Agency said.

Rebels broke up into small groups to elude troops who overran a rebel training camp Sunday in the foothills of the Sierra Madre Mountains in Bulacan province about 20 miles north of the capital, said the government-run People's Television station.

It did not specify how many troops were added to the approximately 1,000 who have been searching the area for rebels since Sunday.

Brig. Gen. Eugenio Ocampo claimed Tuesday that at least 20 New People's Army guerrillas have been killed in the operation. He acknowledged the figures were based only on reports from local civilians, and that fewer that 20 bodies of slain rebels were recovered.

Troops who overran the rebel camp found abandoned weapons, clothing, medicine and ''subversive documents,'' including a list of local officials targeted for assassination, Ocampo said.

The main rebel force split up into several units, the television station said, adding that two groups were spotted near the villages of Baraca and Marungco. It did not say when the rebels were sighted but quoted military officials as saying they were heading for Manila.

Lt. Col. Pagasa Fausto, commander of an air force group assigned to defend the capital, told the station he had set up blocking forces in at least three strategic places south of Bulacan's Angat River.

''Most probably, they (rebels) have intentions to join up with their friends in the capital region,'' he said.

Fighting in the 18-year-old Communist insurgency increased after peace talks broke down and a 60-day cease-fire expired Feb. 8.

More than 700 people have been reported killed so far this year in what the military calls ''insurgency-related incidents.''