Two duels - one visible, the other less so - lie at the heart of Philippine politics today. The visible struggle is between the opposition - in the streets and the new National Assembly - and the government of President Ferdinand Marcos. The other duel is inside the opposition itself, between moderates and the tightly organized, highly committed activists of the underground Communist Party of the Philippines.
Both duels are intense and in the long run equally important for the future of the Philippines.
For the time being at least, the second contest is distinctly lopsided. The moderate opposition is divided and disorganized; it seems only dimly aware of the strength and aims of the communists; and it appears to have lost the initiative it gained after last May's election upset, when 59 opposition members were returned to the National Assembly.
The left, on the other hand, has recovered from what one Communist Party cadre calls its ''tactical defeat'' in the elections. (The party had maintained its traditional attitude of boycott.)
It is now more confident than ever. ''Conditions have never been as good as they are now for a decisive victory by the end of the decade,'' a longtime party member said.
Both the left and the moderates are setting their sights on 1987, but for starkly different reasons.
The moderates hope to defeat President Marcos or his nominee in the presidential elections due that year. They plan to use the local elections of 1986 to build and test a political machine.
The Communist Party, on the other hand, plans an intensification of political and military activities throughout the country, culminating in 1987 in what it calls a ''first quarter storm'' - a reference to the violent demonstrations in Manila during the first three months of 1970 which rocked the regime. Those demonstrations were probably a major factor in Marcos's decision to declare martial law in September 1972.
By then the Communist Party plans to have armed units - known as armed city partisans - active in the city on a regular basis. Communist sources say that activities in the capital will be accompanied by an increase in armed actions in the countryside by the party's armed wing, the New People's Army (NPA).
By 1987, the party says, NPA units throughout the country are expected to be operating in company-sized units - 100 or more fighters. At present they are only doing this in major strongholds like the southern island of Mindanao.
NPA guerrillas also plan to launch ''local uprisings'' in smaller urban areas , seizing government offices and temporarily paralyzing the administration. And by the time the storm breaks in Manila, a Communist Party source says, ''If all goes according to plan, we should be able to disrupt the economy enough to worry the IMF (International Monetary Fund).''
Though it rejects the idea of attaining victory by parliamentary means, the Communist Party is considering covertly fielding candidates in the local elections of 1986. Proponents of this idea in the underground feel that having sympathizers in the local government would make it easier for the party to expand both political and military activities.
Political assassinations, commonplace in the provinces, came to Manila this May with the killing of Brig. Gen. Tomas Karingal. A Communist Party source said that General Karingal had been killed because of his ''notorious anti-labor attitude'' - his men had been involved in the violent breakup of a number of strikes. Other senior officers are marked for assassination, the source said - among them, it was hinted, the senior police officers assigned to handle demonstrations.
Some NPA guerrillas and cadres have already moved into Manila.
They are being used as the core of what the left calls ''composite units'' - militant and apparently well-disciplined students, workers, and urban poor who have been literally in the forefront of recent demonstrations.
In one recent rally, on Aug. 17, composite units ignored moderate leaders headed by Agapito (''Butz'') Aquino - brother of the assassinated opposition leader Benigno Aquino Jr. - who were negotiating with police officers. In a maneuver that impressed observers with its discipline and precision, the demonstrators marched straight for a police line and after a tense confrontation were allowed to proceed. Later a Communist Party source explained the demonstrators' discipline.
''In each of the first 10 or so rows,'' the source said, ''we had someone from the countryside'' - that is, a guerrilla.
Leftist organizers say these demonstrations are ''muscle-flexings,'' preparation for tougher things to come.
Moderates have tended to view the left as a constituency to be won over, not as a competitor with its own agenda. They also seem to overestimate the drawing power of their own personalities, and underestimate the strength of the left's discreet, anonymous leadership.
This complacency is typified by Aquilino Pimentel, head of the Pilipino Democratic Party and a probable presidential candidate in 1987. Looking down from the grandstand on the sea of flags, many of them red, as demonstrators gathered in a Manila park on Aug. 21 to mark the first anniversary of the Aquino assassination, Mr. Pimentel denied that the left would be a problem.
''The left these days follows Butz (Aquino),'' Pimentel said. ''Whatever Butz says goes.''
Shortly before this the left had disobeyed Butz by organizing a lightning side-demonstration. ''They keep on doing that,'' Aquino said, ''and they have their own hidden agenda.''
Aquino says that demonstrations in Manila on Sept. 21, the 12th anniversary of the declaration of martial law, mark the end, ''or at least the loosening,'' of his relationship with more radical groups. He says he is thinking of organizing a new grass-roots-oriented party.
But the left has been organizing the grass roots for many years already. Last week Butz and some advisers sat over lunch brainstorming names of potential core members of the new party. Several of the key ''sectoral representatives'' they mentioned already had close affiliations with the underground.
At the moment the Communist Party feels that it is in a no-lose situation. The present political climate gives it leeway to continue its clandestine and semilegal organizing work among students, laborers, and professionals.
Given his need for foreign credit, party strategists feel, Marcos is unlikely to reimpose any form of martial law. If he does, however, the party feels that it will benefit once again from the subsequent political polarization: The 10 years of martial law were years of rapid growth for the communist underground.
One aspect of the present situation is especially helpful, the party feels: Amendment 6 to the Constitution, which allows the president to rule by decree when he sees fit.
This, a Communist Party cadre noted, constantly undermines the National Assembly's credibility. ''It's a sort of self-destruct mechanism built into the Assembly,'' the cadre remarked.