MIAMI — CALL it a Cuban version of the underground railroad.
Mingling with tank top tourists on day-trips to the Bahamas, Cuban refugees are slipping aboard luxury cruise ships and riding a deck chair to Miami.
An estimated 100 aliens a week are sneaking into the United States, eschewing the dangerous rickety-raft route across the Florida Strait, according to a senior United States Border Patrol agent in Ft. Lauderdale, Fla.
Nor are cruise ships the only way they are coming in. Last week, a record 62 undocumented Cubans -- the most in a single week -- flew into Miami from Honduras, Costa Rica, and elsewhere, report US officials.
This spurt in Cuban refugees entering the US by third-country routes follows a controversial change in policy announced May 2 by the Clinton administration.
For three decades, Cubans found at sea were brought to US shores. Under the new policy, they will be returned to Cuba.
But those who make it to the US undetected -- on cruise ships and by any other methods -- will be allowed to stay in the US.
With the new policy, the problem of smuggling illegals on cruise ships ''is only going to get worse,'' says the US Border Patrol agent, requesting anonymity.
The Border Patrol, the INS, and many cruise-line executives are well aware that lax immigration inspections on cruise ships allow Cubans and other aliens to enter the country undetected. But it's feared that tighter enforcement could hurt business.
''Tourism is big business in southern Florida. Conducting inspection at landside means long lines, and long lines mean unhappy tourists,'' says Hector Kingley, a senior INS inspector performing en route inspections aboard a recent cruise.
Cruise-ship executives say they're beefing up inspections in light of the policy change for Cuban refugees.
''We are even more vigilant for the possibility of aliens, now that the door has been effectively closed for Cubans,'' says Discovery Cruise Line spokeswoman Roberta Backus. ''Passengers now face greater scrutiny.''
A trip last week aboard the Discovery, however, revealed few noticeable restrictions.
Passengers freely climbed the gangplank in the Bahamas without showing proof of citizenship or being questioned by an INS inspector. And in Miami, upon disembarking, passengers only had to present Customs officials with a completed form indicating if duties were owed on goods purchased abroad. Identity papers were not requested.
The carefree party atmosphere aboard the one-day cruises contributes to making the ships easy passage for Cubans and other illegals. Passengers and crew are mostly foreigners, making illegal aliens difficult to spot. Drinking on the pool deck and later in port is common. Ship crews often just wave drunken passengers aboard.
The en route inspections are carried out by an INS inspector who boards the cruise ship at the port in Florida.
About an hour into the return trip from the Bahamas to Miami, it's announced over the public address system that all nonresidents of the United States must appear in the lobby for an inspection. Illegal aliens who boarded in the Bahamas can ignore this request, however, and are not asked for identity papers by ship or INS personnel.
Cruise ships are levied fines of $3,000 per illegal alien caught on board trying to enter the US.
But only two aliens were caught last year by immigration officials on the Discovery. That number, according to Ft. Lauderdale Border Patrol agents, ''doesn't tell the whole story.''
''Cruise ships don't see the fines as a deterrent -- they're making so much money that they don't bother with additional security,'' an INS agent says.
LAST year, an estimated 700,000 people took day cruises from Miami and Ft. Lauderdale to the Bahamas on the Discovery and Sea Escape Cruise Lines. Cubans and other illegal immigrants find it easy to travel to the many islands in the Bahamas -- either by airplane or boat -- where visa requirements are more lax than US standards.
''In the cruise industry, [the inspections are] considered kind of a joke,'' says Tim Gallagher, a Carnival Cruise Lines spokesman. ''With en route inspections,'' he says, ''the day cruises can't be certain who's on the ship.''
A five-year undercover investigation by the Border Patrol found that day cruises are used by foreign criminal gangs as a means to smuggle aliens and drugs into the US. Although ''Operation Sea Cruise'' ended two years ago after 22 people were convicted of alien smuggling, the lessons learned have yet to be adopted.
''The incentives to change the practice just aren't there,'' says a Border Patrol agent who worked on Operation Sea Cruise. ''The Immigration Service treats day cruises as the least important of their concerns, and the US Attorney's Office in Miami finds little interest in going after smugglers.''