MIAMI — At first glance, Cuba’s business potential looks as pretty as its postcards: A nearly five-decades-long embargo has made the island just 90 miles from Florida’s coast hungry for nearly every good and service a U.S. company might provide.

But the flip side tells a different story about the most populous country in the Caribbean: that of a cash-strapped state with crumbling infrastructure and an economy in the stranglehold of an authoritarian government.

Those conflicting realities, however, are not stopping entrepreneurs from planning for the day when the embargo is lifted — or from taking advantage of business opportunities already permissible under the embargo.

Tourism and telecom firms have been energized by recent regulations promising greater access; port operators and oil drillers are gearing up for a rush; and lawyers and consultants are lining up for a piece of the action. With its broad beaches, stunning colonial architecture and world-class artists, it’s not hard to imagine the island as a tourist mecca.

For Cuba, more foreign visitors would provide access to the quick cash that it needs to jump-start the economy.

The island received 2.3 million visitors in 2008, according to the Caribbean Tourism Organization.

If the U.S. government dropped its travel restrictions entirely, rather than just for Cuban-Americans — and Cuba proved as big a draw for American tourists as Jamaica, the Dominican Republic or Cancun, Mexico — the island could expect more than 1 million additional visitors a year.

Mere curiosity — seeing ’58 Oldsmobiles and giant Che portraits on buildings — could lure many, said Damian Fernandez, a longtime Cuban policy expert and provost of Purchase College State University of New York. But it’s unclear if Cuba could handle the influx. The island has about 50,000 hotel rooms, according to a report released by the Cuba Committee of the Greater Miami Chamber of Commerce.

And while it is making improvements, its phone system, electricity and water-supply infrastructure are struggling.

Cuba’s Old World feel is part of its charm, but many visitors are also looking for modern amenities, said Mark Watson, 30, a tourist from Canada who recently visited the island.

Compared with other Caribbean tourist destinations, he found the island’s food mediocre, prices expensive and his hotel, the Tryp Habana Libre, where rooms start at $168 a night, outdated and shabby.

“I’m not sorry I came here,” he said. “But I will never be back.”

The infrastructure woes may not only scare away visitors but stunt the growth of other tourism enterprises, said Tim Gallagher, vice president for public relations at Carnival Cruise Lines.

“You can take people to the islands, but you have to have a way to transport them once they are there and have tours for them,” he said from the company’s Miami offices. “Whenever Cuba does finally open up, it will take a while to put all that into place.”

The infrastructure challenge is not easily overcome. But rebuilding the island’s infrastructure is where many see the money.

Under regulations issued by the Treasury Department on Sep. 3, U.S. companies can now offer cellular roaming services; satellite TV and radio; and fiber-optic cable to the island.

Sprint and AT&T would not comment on Cuba’s potential, saying they were still studying the rules, but there are a number of telecom companies actively seeking licenses to do business in Cuba.

Cuba’s ally Venezuela is already laying a fiber-optic cable to the island. And Cuba routinely blocks radio and TV transmissions from the United States, which would make U.S. firms unlikely contenders for that market. In addition, the Cuban government already has roaming agreements with European carriers, which make the prospect of U.S. deals more likely.

In the absence of foreign investment, another avenue for Cuba to finance its development would be to sell products to the United States. But there, too, complications exist. Tobacco and sugar could bring in quick cash, but exporting sugar would require the United States to drop sugar quotas. And while Cuba is thought to have as much as a third of the world’s nickel reserves, much of it is locked up in a deal with Canada’s Sherritt International.

Pharmaceuticals and biotech are another possibility, particularly products developed by the Center of Molecular Immunology (Centro de Immunologia Molecular), which has created some potential cancer vaccines and treatments. Washington recently allowed U.S. clinical trials of Cuba-developed nimotuzumab, a cancer treatment that is already approved in some nations.

If the embargo were lifted, some believe U.S. pharmaceutical companies would be more likely to hire Cuba’s best biotech scientists rather than to purchase rights to Cuban drugs. But as long as the Castro government remains in power, top scientists might not be able to leave the country easily.

Perhaps the biggest wild card in the Cuba equation is the prospect of crude.

The U.S. Geological Survey estimates that there are 4.6 billion barrels of untapped oil off northern Cuba, some of it just 50 miles from Florida’s coast. While drilling has been hampered by the global slowdown and Cuba’s cash crunch, companies are moving in, including Spain’s Repsol YPF, Brazil’s Petrobras, PetroVietnam and Russia’s Zarubezhneft. Venezuela’s PDVSA has said it will begin exploring in 2010.

It’s not surprising, then, that U.S. companies are eager to have a piece of the action in their own backyard, said Eric Smith, the associate director of the Tulane Energy Institute in New Orleans. If and when the sanctions are lifted, “Americans will be all over the place,” Smith predicted. “But they’ll also be playing catch-up.”

All of these scenarios assume not only that Cuba wants to do business with the United States, but that the end of sanctions would come with other changes on the island. While the United States has control over if and when it lifts the embargo, it takes two partners to do business.