SANTIAGO, CHILE -- After years of bickering, Chile's opposition parties have agreed to pool their resources in a concerted effort to block Gen. Augusto Pinochet's bid for a new eight-year term as president.

The decision to pool personnel and funds in a joint voter registration drive represents a significant advance toward unity among the country's fractious opposition groups over how to bring about a return to democratic rule.

Since early in the year, several civic and political organizations have been campaigning separately for "free elections," urging Chileans to register to vote as a first step toward restoring democracy.

Galvanized by Pinochet's determination to run for president in a single-candidate plebiscite expected next year, the groups announced at a press conference last week that they would start coordinating publicity and mobilization events, set up a joint team of 100,000 volunteers and establish an independent center to monitor registration and voting.

The accord encompasses a broad spectrum of political parties, from moderate-left Socialists to some members of the rightist National Party. It excludes the Communist Party, which has objected to the registration drive, saying such a step would legitimize the military regime.

"This agreement creates a common apparatus while respecting party differences," said Andres Zaldivar, a senior Christian Democrat and one of the joint campaign's organizers.

In another development this week, the Christian Democrats, the country's largest party, began a lengthy process of formally registering as a party. The controversial move was defended by the party's new right-of-center leadership as both a good faith gesture to the regime and a means of claiming the right to post observers at polling places on election day.

Chile's numerous opposition parties have suffered from policy differences, personality conflicts and lack of money during 14 years of military rule. This year, the government offered to legalize non-Marxist parties and re-register voters.

Despite the new steps toward unity, the parties remain far from agreement on a common platform or a common candidate to run against Pinochet. In the absence of both, Pinochet continues to claim that he represents the best alternative for Chile.

The 1980 Constitution calls for a plebiscite to confirm or veto a presidential nominee who is due to be selected in 1988 by the commanders of the three armed forces and the police. Pinochet has given every indication he intends to be that candidate and stay in power until 1997.

Opinion surveys show less than 20 percent of the population favors keeping the 71-year-old Pinochet. But the government has apparently been counting on a high level of registration among its supporters and a low level among its opponents.

By encouraging more people to register, opposition groups hope to increase the probability of a large "no" vote in the plebiscite and possibly even persuade Pinochet ahead of time not to run.

The registration drive, though, has been slow in getting off the ground and still faces a number of obstacles. Funds for advertising and organizing are scarce. Opposition parties have no legal right to equal time on national television, which the government uses extensively.

Apathy among Chileans is high. Only 2 million out of nearly 8 million eligible voters have signed up since electoral registers were opened in February to replace the records destroyed in the 1973 coup that brought Pinochet to power.

"The principal problem we're facing is that people think it is impossible to defeat a dictator through elections," said Ricardo Lagos, a Socialist leader and another of the campaign organizers.

The government has also made registration expensive for many Chileans. As a first step, a citizen must obtain a new state-issued identity card, which, along with a requisite photo, costs the equivalent of $1.50 -- or more than half a day's pay for an average laborer -- not to mention time lost from work. About 6 million Chileans have obtained the cards, officials say.

Coordinating Pinochet's campaign are officers on his presidential staff and in the Ministry of Interior. They are assisted by appointed provincial governors and mayors who, according to a confidential document distributed to mayors at a closed-door meeting last month, have been instructed to "neutralize" opposition forces, cultivate community leaders sympathetic to the government and use municipal resources to seek electoral support for the regime.

Pinochet's main political threat appears to come not from outside but from inside his own government. He faces resistance from other service commanders who have said the next president should be a civilian. The junta members are likely to proceed cautiously, though, for fear of provoking the Chilean leader into some kind of clampdown.

Gen. Humberto Gordon, the Army's representative on the four-man junta, signaled a possible compromise recently when he told reporters that Pinochet would become a civilian if elected in the plebiscite.

This would meet a growing concern in the armed forces that Pinochet should not risk the prestige of the military by running as the Army's commander-in-chief in a vote he could well lose.