The outlawed Communist Party of the Philippines is maneuvering through front groups to broaden its base of public support and encourage backing of sympathetic candidates in local elections next year as part of new tactics in its "people's war" against the government of President Ferdinand Marcos, according to Communist and military sources here.

The moves reflect an intensified effort by the Communist Party and its armed wing, the New People's Army, to take their 16-year-old guerrilla war into cities in pursuit of the party's goal of establishing a "democratic coalition government." The party has scorned electoral politics until now.

"We cannot win the war in the countryside," a party official said in a clandestine interview here. "The enemy is in the cities."

The party and its guerrillas already have made major inroads in Davao, the Philippines' third-largest city. Communist political cadres and guerrilla assassination squads called "armed city partisans," or, more popularly, "sparrow units," seem to operate here almost with impunity. Even government officials, notably Defense Minister Juan Ponce Enrile, have described Davao as a testing ground for the nationwide Communist rebellion currently being waged by about 12,000 guerrillas.

The guerrillas have become increasingly active in other cities on the southern island of Mindanao and have moved to take advantage of abysmal economic conditions, including widespread malnutrition on the central island of Negros, because of a severe slump in the sugar industry. According to military sources, the guerrillas also have begun to probe Manila with a view to setting up their death squads, although police say these plans so far have been foiled.

Instrumental in the party's drive to lay the groundwork for the eventual "urban uprisings" it forecasts is the National Democratic Front, a shadowy self-styled coalition of "Filipino nationalists, democrats, progressive Christians and church people, socialists, communists and other genuine patriots."

In a 12-point "revised draft program" issued earlier this year, the front stressed a number of positions designed to appeal to moderate opponents of Marcos. But it also raised the prospect of revolutionary courts, "severe punishment" or "reeducation" for opponents and large-scale nationalizations if it succeeds in taking power.

The front, which also has been outlawed by the Marcos government, claims to be free of domination by any "single political party or group." But a government white paper issued last month called the front an "operating arm" of the Communist Party, and even sympathizers acknowledge that member groups are essentially controlled by the party.

While the front has failed to broaden its support significantly at the national level, it clearly has become a force to be reckoned with here on Mindanao. According to opposition sources, it has been a leading instigator of strikes and other antigovernment protests on the island.

The front, long in obscurity since its founding in April 1973, has been attracting more attention lately amid rising concerns over the spread of the Communist insurgency and signs of growing public acceptance of the Communist Party as a political force. According to government and opposition sources, party operatives already run shadow governments in many localities.

The white paper says the Communists have "political and military infrastructure" in nearly 1,700 of the country's 42,000 barrios, or villages. Senior government officials have raised concerns that years of fighting, and possibly civil war, lie ahead.

In his latest comments on the insurgency, Defense Minister Enrile told businessmen last week that it would take at least 10 years and "billions of pesos" to stop the rebellion, no matter who is president. If the government loses its political will in the fight, he warned, "then I sincerely suggest that you start thinking of moving out."

According to a western missionary who has lived here more than a decade, "The middle forces -- the liberal democrats, the human rights people, the labor sector -- are more willing to cooperate and participate in activities that the underground helps to organize. There's more and more willingness to work together. A radicalization is taking place."

For its part, the Communist Party also appears more open now as it seeks to put its views across and persuade moderate anti-Marcos politicians, students, workers, professionals, businessmen and Roman Catholic clerics to support revolutionary change leading to a future coalition government with the Communists.

"We intend to politicize the moderates," said the Communist Party operative interviewed here. The official, who goes by the code name of Islao, said a "majority of moderates" already were working against the government.

"We want to be in on the final reckoning, because if we leave everything to the Communists, we might be left out," said an opposition lawyer. "We have to be there so at least we can moderate the outcome," he said. The problem, he said, is that the Communists are in a much stronger position to call the shots because they can always fall back on the guerrillas.

Islao, however, insisted that if the rebels win, "it does not mean a one-party state." The interests of moderates and various other groups can be represented through the National Democratic Front, he said.

It is through the front that the Communists now are beginning to organize for participation in local elections scheduled for May 1986 in a reversal of a boycott policy during the parliamentary elections last year, according to government and opposition sources. The boycott was largely a failure; a majority of voters turned out to elect 183 legislators, including 60 moderate opponents of Marcos.

Islao acknowledged that "we might be able to support candidates" in next year's elections of provincial governors and local officials. But he stressed that "we have no intention of supporting anyone from among our comrades," and he made clear that participation in the elections would be merely a tactic in the "protracted people's war."

"It's only a tactical way of helping the people. An election is a style of change that changes only the branches and not the roots," Islao said.

Islao, 31, made the statements in a secluded restaurant here in the presence of two youths whom he identified as "armed city partisans," members of one of the New People's Army liquidation squads active in Davao.

During the interview, Islao referred repeatedly to the National Democratic Front's revised draft program.

The manifesto pledged to "terminate all unequal relations with the United States and other foreign entities," cancel the U.S.-Philippine Mutual Defense Treaty and make U.S. forces vacate two large naval and air military bases. "No foreign power shall be allowed to set up military bases on Philippine soil, nor to carry, by any means of transport, nuclear weapons into Philippine territory," the document said.

"As a rule," it continued, "direct investments and profit-making assets of the United States and other big foreign capitalists, especially those in the vital and strategic industries, shall be nationalized." Compensation or exemptions would be negotiated "where necessary."