JACKSONVILLE, Fla.--Leaders of the Medellin Cartel masterminded the slayings of Colombia's justice minister and the top U.S. drug informant, according to a cocaine-trafficking indictment unsealed here yesterday.

Among those indicted were a Massachsuetts man and Everette Bannister, a close associate of Bahamian Prime Minister Lynden O. Pindling. Bannister was accused of taking money from the cartel to allow traffickers to use the island nation off Florida's shores as a way station for $1 billion in drug imports.

The case "once again shows that the United States is not going to let up our efforts to catch these individuals who are supplying drugs to the United States," U.S. Attorney Robert W. Genzman said. "We feel that the pressure has got to be kept on regardless of how many indictments come out in the United States against members of the cartel."

In all, 30 people were charged in the "second wave" of indictments resulting from last May's conviction of Carlos Lehder Rivas, one of the leaders of the cartel, which officials say is responsible for up to 80 percent of the cocaine imported into the United States.

The indictment accuses cartel leader Pablo Escobar Gaviria of organizing the assasination of Colombian Justice Minister Lara Bonilla on April 29, 1984, and says Escobar and Fabio Ocho Vasquez directed the February 19, 1986 slaying of former Drug Enforcement Administration informant Barry Seal.

Other major figures indicted were cartel kingpins Jose Gonzalo Rodriguez Gacha, Jorge Ochoa Vasquez, Fabio Ochoa Vasquez and Gonzalo Mejia.

Most of the cartel members were indicted earlier in Miami, but none have been taken into custody.

Genzman said the indictment covers a 15-year period from 1974 to the present, and involved the importation of 44,000 pounds of cocaine, worth $1 billion.

"The indictment contains 205 snapshots of a long-term drug conspiracy in action," he said.

Also indicted was Jack Carlton Reed, co-defendant of the cartel leader.

Lehder and Reed were convicted here last year of conspiring to import cocaine. Lehder--an unindicted co-conspirator in the new indictment--is currently serving a life sentence and Reed is serving a 15-year term. His former wife, Yemel Nacel, is also among those indicted.

"The indictment traces Lehder's development into a primary overseas transporter of cocaine for other Medellin Cartel members, and his continued association with these members after they developed their own transportation operations," Genzman said.

The indictment accuses Escobar, Rodriguez, Mejia, Reed and the two Ochoas of running a continuing criminal enterprise--punishable by a maximum life sentence--and conspiracy to import drugs.

The indictment alleges that after the slaying of Bonilla in Colombia, top cartel leaders fled Colombia and eventually traveled to Nicaragua. They allegedly stored 1400 kilograms of cocaine at Los Brasiles Air Force Base in Nicaragua before flying it into the United States.

Bannister, who lives in Nassau, is charged with receiving bribes to allow the cartel to use the islands just off Florida's shores as a way station for drug shipments.

Bannister could not be reached for comment in Nassau. Bill Kalis, a spokesperson for Pindling's office, did not return a telephone call.

Genzman said the United States has an extradition treaty with the Bahamas and would seek custody of Bannister. He refused to answer questions about continuing allegations that Pindling himself was involved in the drug operation.

As for the cartel leaders, the U.S. attorney noted that it had taken six years to get Lehder to the United States.

Bannister was charged in August 1985 with two counts of perjury for lying to the Royal Commission when he denied taking bribes from a drug trafficker. The charges, however, were dropped when the Bahamian attorney general refused to give the trafficker immunity from prosecution.

Several witnesses in the Lehder trial testified that they had made payoffs to high Bahamian officials, including Pindling, who has denied the allegations.