Once again, some Cubans who planned to motor across the Florida Straits in a converted automobile were stopped short of their goal.

Eleven Cubans in a vintage Buick -- three of them the original ''truckonauts'' who tried a similar intrepid journey last year aboard a battered Chevy pickup -- were intercepted by the U.S. Coast Guard early Wednesday and now face a return trip to the communist island.

The Coast Guard declined to comment on the fate of the car or its occupants, citing a policy not to comment on an ``ongoing mission.''

But exile leaders said they have been told the Cubans will be repatriated.

''We've appealed to the State Department asking them to allow these people to stay,'' said Joe Garcia, executive director of the Cuban American National Foundation.

Arturo Cobo, an exile activist in Key West whose refugee center helped thousands of rafters in the 1990s, said he reached out to government contacts on behalf of the Buick's passengers -- but was told it was too late.

''My sources tell me that, like the truck seven months ago, this car has also been sunk by the Coast Guard, and the people on board will be repatriated back to the island,'' Cobo said.

Garcia, too, said he had information the '59 Buick had been swallowed by the sea.

U.S. Rep. Ileana Ros-Lehtinen said her office had been contacted by constituents worried about the plight of the 11 Cubans -- and offering to buy the Buick ''that was valiantly sailed . . . to illustrate the ingenuity of the Cuban people,'' the congresswoman said in a letter to President Bush.

The Buick, painted sea-foam green and fitted tightly in a boat prow, was spotted Tuesday north of Cuba. By nightfall, the tail-finned vehicle had made it more than halfway to Key West.

A source familiar with Coast Guard communications said that when the Cubans -- six adults and five children -- realized they had been spotted, they piled into the vehicle and rolled the windows up tight.

TRY, TRY AGAIN

Among the adults in the car were childhood friends Marcial Basanta López and Luis Grass Rodríguez, as well as Rodríguez's wife, Isora.

The three were among the 12 Cubans spotted in July in the now-notorious 1951 Chevy pickup, whose failed attempt to flee the island earned international attention and the nickname camionautas -- or truckonauts.

But by the time images of the floating Chevy were beamed across the globe, the 12 Cubans had already been sent home, the truck sunk in a spray of Coast Guard machine-gun fire.

Although he would not comment on the fate of the sedan, Coast Guard spokesman Luis Diaz said Wednesday the decision to sink the Chevy was based on standard safety concerns.

''If it's a hazard to navigation, it's too dangerous to leave in the water,'' he said. ``We do that with any vessel that is not seaworthy, which has included drug boats and migrant rafts.''

The sinking of the Chevy -- and the return of its occupants to Cuba -- sparked outrage from exiles and vintage car buffs alike.

Once back in Cuba, Basanta and Grass -- now without a truck to perform errands for meager incomes -- once again found themselves desperate and searching for another way out of Cuba.

A friend, identified only as Rafael, owned a Buick.

'We would ask why weren't they using the Buick to earn money, and they told us, `It needs repairs,' '' said Lourdes Grass, sister of Luis, from her home in Havana's San Miguel del Padrón. ``I guess those were the repairs they were making. Pretty intelligent, no?''

Lourdes Grass said the Buick's planned journey was a tightly held secret in the neighborhood -- even among family.

'I had no idea. They would never tell us. We would ask, `Why are you coming home so late every night?' '' she said. ``Luis would just say he was working, that he needed to make whatever money he could.''

But under cover of night, Basanta, Grass and a few co-conspirators worked on the Buick's cruising potential.

Last year, Basanta was too afraid to bring his wife, Mirlena, and their school-age son and daughter aboard the Chevy.

''But they persecuted them so much, he had to take them,'' said sister Oramia Basanta López, speaking by phone from Cuba.

UNDER WATCH

Relatives say the homes of the mechanics were periodically raided by state police. Basanta's phone line was taken out. Tractor parts were confiscated by security agents, who cited concerns of another automotive bid for escape.

Lourdes Grass said the gifted tinkers -- well-practiced in maintaining the prerevolutionary automobiles that chug through Cuba's streets -- used the same mechanical plan on the Buick as on the Chevy, save for a few design changes.

''I'm told it is the same design as the first: They crafted propellers and attached them to the drive shaft, and used the original car motor to go,'' she said.

But the '51 Chevy was kept afloat by a makeshift pontoon fashioned from steel drums.

The Buick -- at first mistakenly identified by the Coast Guard as a Ford Fairlane -- was tucked into a boat prow painted the same shade of green as the car's body.

The interior of the Buick had been welded water-tight, and the hard-top, tail-finned car still had its wheels when it embarked around 8 p.m. Monday, slipping away from the Cuban coastline, relatives said.

The Chevy still had its tires, as well.

Basanta, speaking last year with The Herald after his return to Havana, explained the group's reason for leaving the Chevy roadworthy: The Cubans planned to pop off the pontoon once they reached shore, and drive to a relative's home in Lake Worth.

The cousin who expected their arrival, Kiriat López, spent Wednesday frantically phoning relatives, hoping for news of his cousin.

''They have earned their way into this country, just by what they have managed to do,'' López said. ``What more do they have to do to show how desperate they are?''