Hoping to grab some of the limelight of a summit of foreign leaders in Havana next month, Cuba's small dissident movements are planning their biggest burst of public defiance since Concilio Cubano in 1996.

Repressed and infiltrated by security agents, opposition leaders admit they are more likely to end up in jail than anywhere near the Iberoamerican summit Nov. 15-16.

Some 30 dissidents have already been detained or harassed in the last two weeks in an apparent government signal that it will not allow any disruptions while the foreign leaders and journalists are in Havana.

But opposition leaders said they cannot let slip the chance to throw their moral weight against the communist government and present their demands for freedom to the heads of state from Latin America, Spain and Portugal.

''Everyone, in some way, is preparing to take advantage of the summit to publicize their positions, said Elizardo Sanchez, head of the Cuban Commission for Human Rights and Reconciliation.

One Western journalist in Havana reported his phone has been ''ringing off the hook with calls from dissidents announcing press conferences or statements addressed to the heads of state or President Fidel Castro.

DETAILS FUZZY

One faction is planning the largest dissident gathering since security agents broke up the Concilio Cubano coalition by arresting some 200 members in 1996, but is keeping details fuzzy in hopes of avoiding a police crackdown.

''The plan is to bring together as many groups as possible, hear their positions, draft a short joint statement and have it ready for when the summit starts, said one dissident involved.

Another group is working discreetly to meet with Spanish President Jose Maria Aznar, which would boost the dissidents' international standing, while other dissidents have been trying to organize acts of civil disobedience.

Several other groups already have issued public statements on the summit and announced plans for press conferences and ''seminars around the time of the gathering -- one even boldly inviting Miami exiles to attend.

A collection of some 20 small dissident groups, the Third Millennium Forum, has urged summit leaders to force Castro to observe the agreements on democracy they all signed during a previous summit in Chile.

''We hope the government understands that on the eve of the Third Millennium . . . intransigence, intolerance and despotism must, for the good of all, give way to reconciliation, said a Forum declaration Oct. 2.

'CONGRESS' PLANNED

The National Coordinator of Cuban Prisoners and Former Political Prisoners has invited foreign diplomats and journalists to its upcoming ''Congress, but said it will reveal the exact date only at the last minute to avoid possible police attempts to block the gathering.

The Round Table of the Moderate Opposition, made up of five small dissident groups, issued a 54-page document last month urging Castro to begin ''a gradual transition, without exclusions, toward tolerance and democracy.

And a tiny group of private farmers has scheduled a grandly named ''National Encounter of Independent Farmers and Cooperative Members, in the central province of Matanzas for Nov. 12-14, just two days before the summit.

The organizing committee invited exile figures Willie Chirino, Gloria Estefan, Carlos Alberto Montaner and Agustin Tamargo to attend, even though the Cuban government is highly unlikely to allow them to enter the island.

Cuba's government has steadfastly denied the existence of ''dissidents on the island, calling them all ''counterrevolutionaries paid by the U.S. government to stir up trouble and undermine the Iberoamerican summit.

U.S. State Department officials said Washington has certainly ''encouraged those foreign leaders going to Havana to meet with the dissidents and hear their complaints.

MIAMIANS CAMPAIGN

In Miami, Cuban exiles launched a campaign Thursday to discourage participation in the summit. Twenty-seven exile organizations signed a letter sent to the countries asking for their support and solidarity in not recognizing the Castro government.

''It is inconceivable that as we approach the 21st Century, democratically elected heads of state agree to meet in a country ruled by a dictator that has not held free elections in 41 years,'' the groups said at a news conference.

The presidents of Costa Rica, El Salvador and Nicaragua are boycotting the summit because of Cuba's lack of democracy, while the leaders of Chile and Argentina are staying away because of Spain's effort to bring to trial former Chilean ruler Gen. Augusto Pinochet.

Cuban dissidents acknowledge their weaknesses -- their lack of protection from government repression, their small numbers, the state security agents infiltrated in their midst and their internal feuds.

''We cannot allow internal rivalries or conflicts, nor a certain tendency to exaggerate the dimensions of the plans for a burst of defiance in advance of the summit, one dissident journalist reported from Havana recently.

But they are hoping that their planned activities will force Castro to either take a cautious approach while the foreign leaders are in town, and allow a measure of public dissent, or risk the publicity of a crackdown.

Some 800 foreign journalists have signed up to cover the summit.

RESPONSE EXPECTED

The dissidents' bet: Castro will try to break up the activities as quietly as possible, putting some dissidents under house arrest, denying transportation to others and detaining those who insist on carrying on.

Elizardo Sanchez said he fears even worse -- a harsh crackdown that will reverse five years of ''low-intensity repression that had allowed Castro's opponents some space for complaints.

''It looks like they are getting ready to raise the wall, lift the drawbridge and reinforce the image of a besieged citadel, Sanchez, considered a moderate, said in a phone interview from Havana.

Among the signs he perceives: increased police presence on the streets; fewer permits for dissidents to travel abroad; recent spats with Canada, Portugal and the European Union; and Castro's recent decision to pump an extra $20 million into the government-controlled mass media.

''A government preparing to open itself doesn't do this, Sanchez said. ''I hope I am wrong, but I think we should be preparing more for a hardening than a moderation of the government's domestic policy.