Nearly 900 U.S. and Bahamian agents in boats, planes and helicopters completed a military-style assault on drug sanctuaries in the Bahamas yesterday in a test of cooperation with that island nation, which has become a major way station for South American narcotics.

The unprecedented 16 days of raids, which ended yesterday, netted 5,500 pounds of cocaine and 33,872 pounds of marijuana -- worth more than $100 million -- and brought 58 arrests, U.S. officials said.

Surveillance by U.S. agents in 50 Navy boats was so widespread that the dragnet also snared 600 Haitian refugees seeking to make their way to the United States, officials said.

"Operation Blue Lightning" involved all branches of the U.S. military, the Drug Enforcement Administration, the U.S. Customs Service and more than 20 other federal, state or local agencies, as well as the closest cooperation yet with the Bahamian Defense Forces. It utilized more than 30 aircraft and a half-dozen radar facilities.

Sam Billbrough, associate special agent in charge of the DEA's Miami office, said U.S. agents monitored small-craft movements for two months prior to launching the raids.

"We had surveillance on every entrance from the ocean from West Palm Beach to Key West," Billbrough said in a telephone interview from Miami.

"The Bahamas serve as a staging area to bring drugs into the United States " from Colombia, Jamaica and Belize, he said. Since part of the Bahamas is as close as 50 miles off the Florida coast, he said, "It's been a transient location for refueling, repackaging and transferring drugs."

The raids were planned after a February White House meeting attended by Vice President Bush and two Bahamian ministers. Officials said relations between the two countries had been cool since news accounts of some Bahamian officials acquiescing in the drug trade.

Bush, who heads a federal task force on drug-trafficking in South Florida, praised the operation as "an unprecedented effort to seal off the Florida coast to smugglers." He called the drug seizure "a significant achievement."

Herbert Walkine, permanent secretary of the Ministry of National Security in the Bahamas, agreed. "We are trying very hard to do something about the problem," he said. " . . . We want to be rid of all drug traffickers in the Bahamas. We don't want them there."

Billbrough said that Bahamian authorities made the arrests on island territory, but that the authorities were taken there on U.S. boats and planes piloted by American military personnel, and that they were accompanied by DEA advisers.

The initial assaults targeted suspected drug caches hidden in sparsely populated islands, marshes, forests and caves, Billbrough said. Bahamian and U.S. Coast Guard vessels surrounded 30 selected islands, maintaining roving patrols and waiting for the traffickers to emerge.

Billbrough said the cocaine seized is nearly three times the average monthly confiscation in the South Florida region. He said that the Americans and Bahamians arrested are mainly low-level drug runners, but that investigation into their suppliers will continue.

The operation first came to light last weekend when tourists returning from Bimini, 50 miles east of Miami, told of drug raids by Coast Guard and Bahamian authorities.

"They . . . searched every American tourist vessel, with machine guns," Keith Loring, a University of Miami student who was visiting Bimini, told United Press International.

"They had us open every single compartment, every single boat; then they went on land and searched every boat that was tied up to the docks," he said.

Authorities also confiscated property worth $1.4 million, including 25 boats, two aircraft, two vehicles and a trailer, officials said.