With all the clubbish zeal of middle-class suburbia in the United States, Cuba has become a nation of joiners.In place of the Rotary Club, the bridge club and the Young Republicans, Cubans fill their after-work hours with the Young Communist League, the Cuban Women's Federation and neighborhood Committees for the Defense of the Revolution.

Most city-dwellers attend some sort of community meeting at least two nights a week including special "parent schools" where parents learn what ideology they should be teaching their children outside the classroom, and trade union "emulation" sessions, where workers set common goals and chastise one another for not meeting them.

Idleness and isolation, while not necessarily considered counter-revolutionary, are viewed here with some suspicion, and the organization spirit is infused at an early age. When children are not putting in one of their frequent stints at a local Pioneer Youth Camp, they are "incorporated" into useful group tasks, including house-to-house bottle collections or neighborhood patrols to ferret out electricity-wasters among their parents.

The most pervasive mass-membership "clubs" in Cuba are the nation's 7,000 Committees for the Defense of the Revolution. A nationwide network of block and community groups under provincial and national-level unbrellas, they plan and regulate nearly every aspect of daily life.

Every urban neighborhood and rural zone in Cuba has its own committee, or CDR and while membership is not mandatory, CDR regional officials say that those who do not join are subjected to such intense proseletyzing that few hold out for long.

Originally developed in 1960 as a sort of neighborhood militia system for national defense, the CDRs now mastermind neighborhood activities ranging from vaccination programs and cleanup campaigns to anti-crime patrols and demonstrations of public support for Cuban troops fighting in Angola.

While disenchanted revolutionaries occasionally complain that the committe system is a nuisance that has divided Cuba into neighborhoods of hyperactive busybodies, interfering in one another's private lives, such comments are usually made only in off-the-record whispers.

CDR No. 7 in Conscription Zone No. 23, a residential part of central Havana, has 138 members, or about 80 per cent of the residents of its area. On a hot and humid night last month, No. 7's 14-member executive committee met at the home of a member to explain its activities to several American visitors.

"We meet to decide on tasks for the members," said No. 7's "ideological front" director, a rotund, cigar-smoking man whose title is far more intimidating than his appearance.

Among his ideological tasks is the distribution throughout the neighborhood of "study materials" printed by the government to inform the people of new economic or cultural programs.

"We argue in favor of or against a program, vote on it, and if there is a clear majority, submit our opinion to higher levels of authority," he said.

While there is no evidence yet that popular objections can cause changes in government policy, there is little doubt that Cubans study and feel themselves informed about the information the government does hand out.

Next in importance to ideology, an elderly man explained to the visitors, is the CDR's "vigilance front." Each night, a group of committee members - "men, women and elderly people" is assigned to neighborhood guard duty in the schools, banks, grocery stores and other commercial establishments.

The idea, he said, is to prevent street crime through the presence of a guard. The CDR patrols are unarmed and have no arrest power, but keep in constant contact with police.

Should the need arise, the guard squads can also be turned to military duty.

"We are confident that at any threat, all members will rise to the defense of the nation," the elderly man explained. "They are revolutionaries, and are not afraid of any objectives."

While the "Public Health Front" makes sure that pregnant women visit their doctors regularly and monitors the health of children, members of No. 7's "Education Front" visit neighborhood schools "to make sure that parents are giving their children correct ideological orientation."

The children themselves, and executive board member explained proundly, are also trained in productive work.

"They participate in our cultural activities, and learn to respect their homeland and our [revolutionary] martyrs," he said.

The children also organized into something called "Click Patrols," a nationwide effort to cut down on electricity wastage by sending youngsters door to door, "to surprise the neighbors and tell them they have turned on too many lights."

On the "social front," CDR No. 7 counsels the families of members who "need help incorporating themselves into society - a worker who wants to be lazy at the expense of his family." The Social Front also assists families with members in prison, and helps exconvicts "incorporate themselves into revolutionary jobs" on release.

The CDR also organizes letter-writing campaigns to "international fighters" in the Cuban army services abroad, plans welcome-home ceremonies for neighborhood heroes and makes sure that all 16-year-olds registers for the military draft.

"Perhaps the day will come when we don't have so many meetings," said a young woman member of No. 7's executive board with a sigh. "We have to take into account that we are under a revolutionary government and we have a lot of work to do."

But life in a Cuban neighborhood is not all work and no play, a government official in the neighborhood meeting said. "Sometimes when we meet, it's just a neighborhood visit, like you probably have in the United States. We drink coffee, and talk. Sometimes we have to meet just so that we can report that we've had a meeting."