Communist insurgents have expanded their influence and stepped up guerrila warfare on the island of Samar in the east-central Philippines, prompting the government of President Ferdinand Marcos to send in additional military forces.

The insurgents have staged a series of raids on villages on Samar, seizing guns and other equipment from police and holding meetings with the islanders.

Although their numbers are small, the insurgents have been successful enough to worry the government and its military officers stationed here, across the San Juanico Strait from Samar.

The chief of military intelligence for the region, Lt. Col. Pablo Gamban, said that the rebels have been more successful among the 1.1 million people of Samar than anywhere else in the Philippines.

In mid-May Marcos ordered his military forces here to "step up the action" against the insurgents. With about 4,000 troops and police already in the region, Marcos has since ordered three more battalions, about 2,400 combat troops, sent to the area, along with the Air Force and naval support units.

The reinforcements will make this the most heavily protected area of the country outside the southern provinces where the government is attempting to crush the long-running rebellion of Moslem insurgents.

The government's main battleground against Communists in the past has been in the northern areas of the main island of Luzon. After Marcos declared martial law in 1972, a number of party members fled to the countryside and insurrections began on both Samar and Mindanao, to the south. Communist activity has slowly, but steadily, increased in both areas ever since.

Just as Marcos announced the increase of military forces on Samar last month, a new incident underscored the ability of Communist forces to take the initiative. The town hall of Matuginao, a village in northern Samar, reportedly was occupied by 127 guerrillas, who held a day-long antigovernment session with the citizens. They also divested the town police of their weapons, radios and typewriters.

A month earlier, about 70 Communists raided two other town halls and seized weapons from local police. until the occupations of Matuginao, they were regarded as the largest raids ever staged by Communists in the Philippines.

It is believed that the Communists had only a handful of members operating in Samar in 1973, when the buildup began.Their numbers are now estimated at 200 full-time party members and about 500 armed guerrillas. The Communist Party of the Philippines is thought to have about 3,000 active members in the entire country.

The movement on Samar is now so well entrenched that it has become a training ground for young party recruits from Manila universites.

The series of incidents began in 1977 when Communists briefly occupied a county seat and held a public trial for the police chief before executing him. Las February, in a widely publicized incident, the son of the Philippines Army's chief of staff was killed while leading a patrol in an attempt to capture a Communist communications post.

In their more routine activites, the Communist insurgents set up local commands in an attempt of win over villagers and some of the Samar's 200,000 farmers, most of whom are very poor. At first, an armed propaganda unit with a half-dozen party members experienced in farming, health and education is filtered in.

The villagers' reception is not always cordial. Freddie Bravo, a party member captured recently by the government, said in a prison interview that when the propaganda unit first appears "the peasants don't sympathize with having an armed band around because of past bad experiences with armed men." He said that relations improve gradually as the party workers begin to treat illnessess and deal with local problems.

Eventually, the party attempts to build a local following by selecting leaders from among the poorest farmers for more intensive propaganda and training. One of the major projects has been to force landlords to reduce rent paid to them by peasants who till the land. CAPTION: Map, no caption, By Richard Furno - The Washington Post