MIAMI — For Cuban exiles who have dreamed of returning to their native island, Havana looms like an Atlantis, an irretrievable city of legend and lore. Now some 200 architects, art historians, collectors and other devotees of Cuban culture have formed an organization called Cuban National Heritage, whose goal is to halt the rapid disintegration of the country’s architectural riches. The Miami-based group, led by a veteran of the Bay of Pigs invasion, has obtained aerial photographs and block-by-block maps of the Cuban capital, originally prepared for its Communist rulers. But instead of using the documents to wage a new offensive against Fidel Castro, the organization sees them as a valuable tool in its architectural preservation drive. President Clinton’s Oct. 6 executive order easing travel to the island by Cuban-Americans will help Cuban National Heritage step up its activities. The self-styled trust-in-exile, established two years ago and supported by contributions from its members, including wealthy Cuban-born donors, has been dispatching envoys to Cuba to make an inventory of national monuments, urban infrastructures, artworks, archives and libraries. “We are motivated by the urgency of the problem,” said Raul Garcia, a professor of architecture at the University of Florida. “Things are falling down. Everything is disappearing.” Countless Havana buildings are crumbling into ruins, shored up by jerry-built scaffolds and the piece-meal efforts of residents. At risk is what many regard as the finest urban ensemble in the Americas, dating from the 16th century through the 1950s, including prime Baroque and Art Nouveau works. McKim, Mead & White, Carrere & Hastings as well as Le Corbusier-inspired modernists also left their imprint along the city’s European-style boulevards. “Havana is a remarkable museum of first-rate urbanism of importance to the world at this moment,” said Andres Duany, a leading urban planner who is advising the trust. Havana’s architectural significance lies not so much in individual buildings as in the faded splendor of their totality, for the most part untouched by large-scale contemporary real estate development. Situated on one of the world’s great natural harbors, Havana was laid out in a grid pattern radiating from central squares. Other colonial towns in the Caribbean and Latin America imitated this layout, but most have been disfigured by haphazard growth and shoddily built glass towers. Paradoxically, a revolutionary ban on private investment imposed after Mr. Castro came to power 37 years ago has helped keep the city’s finest architecture intact. The Cuban capital, caught in a time warp, retains columned arcades and palm-shaded courtyards in its dense, old-Spanish core. Gracious axial boulevards dominate newer sections that, for all their decrepitude, mirror the cosmopolitan feel of Paris or Madrid. The grandest thoroughfare, the Malecon Promenade, sweeps along the waterfront, its beauty marred by rows of decaying pastel mansions. Dozens of palaces, convents and churches have been restored since 1982, when UNESCO, the United Nations cultural agency, designated sections of Havana as a World Heritage Site. But this effort slowed greatly when Cuba’s economy took a nose dive after the demise of the Soviet Union, Cuba’s major trading partner and benefactor. Desperate for cash, the Government is now seeking foreign investors to salvage the collapsing structures. Washington’s trade embargo against Cuba bars United States investors from participating financially in Havana’s restoration. Nonetheless, concern about the city’s architectural legacy is increasing on both sides of the Straits of Florida; for the first time, people with disparate views of the United States policy towards Mr. Castro have common cause. “The only way to unite Cubans inside and outside is through culture,” said Alberto Bustamante, the Cuban National Heritage president and a physician who formed part of a medical backup team for the failed 1961 Bay of Pigs invasion. In a move toward cultural cooperation, architectural historians and planning specialists from the island have been taking part in trust-sponsored architectural symposiums in Miami and at the University of Florida in Gainesville. (Architectural and informational exchanges are exempt from the trade ban.) For the moment, cooperation is limited. The heritage group has sharply criticized current preservation in Cuba as inadequate and misguided; old stone and masonry buildings collapse on an almost daily basis. In the meantime, the dollar-driven vacation industry sets the tone for restoration efforts. An additional concern of the trust is the swift rise in tourism and the construction of often unsightly resort hotels along the coastline. “The investment is being done by people who do not love Cuba,” said Mr. Duany. “Spaniards, Mexicans, Venezuelans, other people who do not have a patriotic interest in the excellence of Cuba.” Mr. Duany and his brother Douglas, a landscape architect, visited the island in April for the first time since emigrating in 1960. Working from official Cuban maps and photographs obtained through trust contacts, both men are helping the trust devise zoning ordinances to supplement existing ones established to safeguard Havana’s architecture. “We want the codes to be a vaccination against the negative effect of North American-type development,” Andres Duany said. Since the Duanys and most other Cuban-Americans now live amid the suburban sprawl of Miami, trust members know firsthand exactly what they don’t want transplanted to Havana. They fear that powerful South Florida developers, hungrily eying the island, are likely to bulldoze historic areas and build single-family housing projects, condominium complexes and mirrored skyscrapers if given the chance. The trust plans to hold seminars for such developers in the hope of increasing their awareness of what is at stake. But treacherous political waters lie ahead. Militant Cuban exiles in Miami oppose any contact with the island as long as Mr. Castro is in power, at times using the threat of violence to enforce their view. Mr. Castro himself, in a speech last July, seemed to point a finger at groups like Cuban National Heritage, warning of North American academics who he said are trying to “infiltrate” Cuba. Cuban National Heritage insists that it is apolitical. Nonetheless, it is fostering activities outside Government control; in effect, it is encouraging the development of the kind of civil society that human rights advocates see as a catalyst for political change. “There are people on both sides who are interested in working the margins of the Cuban government,” said Douglas Duany.”The problem is that Castro has never tolerated that free space. There’s no politically neutral ground. There is, however, great potential in personal contacts and information exchange.” Not surprising, word that mainland architects and developers are starting to map out Havana’s future has ruffled more feathers than Mr. Castro’s. According to Mario Coyula, director of the Group for the Comprehensive Development of the Capital, a Cuban state planning agency, “What people here resent is to think of Cuban-Americans sitting in Miami, putting in pins and placing Burger Kings and McDonald’s in Havana.” But Mr. Coyula acknowledged that existing zoning laws were inadequate to deal with new foreign investment, which now totals more than $2 billion. “We need to rethink those codes,” he said by telephone from Havana, adding that he was receptive to zoning plans from outside. Isabel Rigol, director of Cuba’s National Center for Conservation, Restoration and Museology, said she, too, was ready to work with the trust, provided it was respectful of work already under way in Cuba. The trust recognizes the expertise of many preservation and planning specialists on the island and cultivates ties with them while trying to avoid direct interaction with state institutions, since it sees this as lending support to the Government. The question is whether cooperation can move beyond the realm of purely academic activity, given current political constraints on both sides. Heritage members say that the moment, interest in the fate of Havana itself provides the most fertile common ground. As Andres Duany put it, “There’s nothing ideological about saving a beautiful city.”