Grove Isle rises against the skyline in towers of opulence, isolated from the problems of mainland Miami by a moat that is Biscayne Bay.

Only a short, narrow bridge links the condominium complex with the rest of the city. The 20-acre island features original sculptures by famous artists in its landscaped gardens and ornate lobbies, apartments priced from $246,000 to $746,000--and security.

The once-booming luxury condo market in Miami has hit a severe slump largely because of overspeculation and overbuilding, and as a result many developers have retrenched from development plans. But one pattern expected to persist through the downturn and beyond is the increasingly elaborate protection systems.

On one recent afternoon, a public relations woman for the complex escorted a visitor from one building to another, identifying herself and her destination to a disembodied voice emanating from a locked door. This is just to get to the sales office.

Guards and closed-circuit televisions and locked doors are part of the draw for Grove Isle, explains sales director Francesco Morello.

"The island, the security, the environment--that's it," Morello says when asked what Grove Isle's attraction is.

The complex is one example of how the upper class in Miami shields itself from the notorious problems that have beset southern Florida--crime and drug trafficking and a flood of Cuban and Latin American refugees.

While local real estate experts say middle-class retirees have started to escape the city, moving farther north, the upper class has another alternative: the fortress condo.

Developers now build "a different kind of building, with lots more security. It's the fortress aspect," said Joseph Kanter, chairman of the board of National Bank of Florida.

Developers here say the perception of crime is worse than the reality here--but they have continued to add layer on layer of elaborate security systems at their luxury complexes and make these a major selling point.

"At Nine Island Avenue, we've installed the most sophisticated state-of-the art electronic security system available today," boasts another island complex in its ads.

"Each apartment has its own two-way TV monitor system. Elsewhere throughout the property, television cameras are positioned strategically providing 24-hour security surveillance both indoor and out. If an emergency situation occurs in your apartment, a security device at your fingertips gives you instant two-way voice communication with a member of our security staff located at the Monitoring Center," elaborates the ad for Nine Island Avenue, which claims that its $170,000 starting price undersells much of the Miami luxury market.

There is also a different kind of condo island--one surrounded by greater Miami but not touched by it.

One such luxury complex is The Towers of Quayside. To get into Quayside, a visitor must be cleared by uniformed guards at the entrance of the complex. Another guard is in a glassed-in booth at the door of each building's lobby, a picture of cool affluence with wood and waterfalls and green marble. Once out in the fenced-in pool area, it takes a special card to get back into the building.

"Security is a very, very important feature," said Stan Cotton, president of his own advertising and public relations firm, which recently has taken on the Quayside account. But Cotton argues that this is true universally, not just for Miami. And, anyway, "there is snob appeal to security," he said. His ads will feature a couple coming back from a safari who need "a safe and simple place to keep our Bentley."

Safe it may be. Simple? No. The compound is a small city to itself, with shops and health facilities and an owners-only restaurant. It has two traveling tennis pros--Bjorn Borg and Vitas Gerulatis.

The average price on apartments there range from $200,000 to $500,000, while villas are priced from $800,000 to $1 million, Cotton said. It would be perfectly possible to stay inside the complex indefinitely.

While violent crime may have created a market for the elaborate security systems in the luxury condos, Miami real estate experts say the condo market has benefited only indirectly from the notorious drug traffic in south Florida.

Drug money has been stashed in south Florida real estate as a favorite investment and so has kept prices high generally, local experts said. But the condo market specifically does not seem to be the recipient of this cash-and-bury system that has become an important part of the south Florida economy, because condo transactions are too visible, they add.

"There has got to be a lot of drug money in the whole thing, but drug dealers are not buying condos as far as we can tell," said banker Kanter.

Charles Kimball, a real estate consultant, estimates that between 15 and 20 percent of all investment in real estate in Dade County is "hot money," either profits from drug dealing or tax evasion. Mainly it goes into land, shopping centers or office buildings, he said, though he believes some has gone into speculation in condominium units.

These illicit funds "give the whole real estate market a lurid, sleazy glow," Kimball said. "If they buy $1 million worth of property, no one is monitoring it" unlike other kinds of investments, such as stocks, he said. "Real estate is the last frontier of unobserved investment."

The cash buyer here generally is the Latin American with "flight capital" brought to the United States to escape inflation or confiscation at home.

This rich Latin buyer has propped up the collapsing real estate market here, even as his poor counterpart--the Latin refugee--has driven some of the traditional buyers away.

Meanwhile, a new standard in luxury markets is being set here--one of all-marble baths and private marinas, original art and famous tennis pros--and million-dollar price tags for a condo enclave from political and social storms.