Posing as shippers and sellers of illegal drugs, undercover U.S. agents have made 29 arrests and disrupted an international marijuana and cocaine cartel by "smuggling" $300 million worth of drugs into the United States, according to Attorney General Edwin Meese III.

Instead of posing as drug buyers, the agents, who learned by studying the Colombia-based cartel that it had no distribution system, posed as transporters and sellers of the drugs, using a "reverse undercover" technique, Meese said.

In one phase of the operation, agents sailed a ship loaded with marijuana from the western Caribbean to the Texas coast. They then delivered the drug and arrested the buyers.

The 12-month investigation, codenamed "Operation Intruder" resulted in 29 arrests in five cities and the seizure of 70 tons of marijuana, nearly one ton of cocaine and $2 million to $3 million in assets.

Detailing the operation yesterday, Meese said it was "one of the most significant" drug cases ever, and he praised authorities in Panama and Colombia for their cooperation in helping to immobilize the cartel, which he said is believed to have supplied 600,000 pounds of marijuana and large amounts of cocaine to the United States over a 10-year period.

The U.S. drug enforcement operation, financed with $2 million of the traffickers' money, was devised in 1986 when undercover agents began negotiating with leaders of the Colombian cartel, Meese said. The U.S. agents established that the cartel had no distribution network in the United States and they volunteered to do the job.

Loads of marijuana and cocaine were shipped from Colombia to the Caribbean and then by the agents to Texas, where the drugs were warehoused before being transported by trailer, driven by agents, to traffickers in Atlanta, Detroit, Denver and West Palm Beach, Fla. Arrests were made at the moment of resale.

In another phase of the probe, Detroit agents flew a plane from Miami to Colombia, loaded it with marijuana and cocaine and then flew to Detroit. The drugs were destined for New York City, but they were seized in Detroit, and nine alleged traffickers were arrested.