Federal authorities announced yesterday that they have broken up what is alleged to be the largest marijuana ring in the country-a paramilitary group charged with smuggling 500 tons of "Colombian Gold" worth $300 million into the United States over the past 16 months.

Fourteen alleged members of the smuggling operation were arrested yesterday on racketeering and drug charges detailed in a 105-page indictment returned by a federal grand jury in Miami.

The indictment charges that the group was run by two businessmen who set up a car dealership to launder millions of dollars in drug profits.

The sophisticated smuggling network included a personal yacht broker, "stash" houses to store the drugs, a communications expert to monitor law enforcement radio traffic as part of a counterintelligence system, a fleet of planes and its own "army" to guard unloading zones, the indictment said.

"They were organized along business and military lines," said Arthur F. Nehrbass, special agent in charge of the FBI's Miami office. He said further indictments are expected from a year-long investigation of drug profits by FBI and Drug Enforcement Administration agents.

A DEA spokesman said the case was especially significant because the alleged smuggling group is so large and because its members were charged under the so-called RICO (Racketeering Influenced and Corrupt Organization) statute, which allows the government to try to seize assets of the alleged racketeers.

The indictment asks that three houses worth $1 million, four yachts, three planes and the South Florida Auto Auction, a used car auction for dealers that allegedly was the "front" for the operation, be forfeited to the government.

The alleged kingpins of the smuggling ring, Robert J. Meinster, 37; Robert E. Platshorn, 36, and Platshorn's wife, Lynne, 34, all of Miami Beach, pleaded not guilty at arraignment yesterday. So did Richard (Chip) Grant Jr., 23, leader of "Chip's Army," the ring's security force, according to the indictment.

The main charge in the indictment is a carefully detailed chronology of the smuggling operation, supplied by informants within the group, according to sources. It reads in places like a movie script. Among the allegations:

At one point after the group had failed at several smuggling attempts, Platshorn allegedly told a pilot he could earn a gold "Black Tuna" medallion like those worn by other members of the organization if he completed a flight.

"Black Tuna" was the code name for Raul Davila-Jimeno, described as the group's supplier in Colombia. Davila, who is still at large, claimed to control the entire Guajira Peninsula and said a Colombian Army colonel and chief of police were on his payroll, the indictment said.

Davila allegedly once paid $300,000 to get one of the leaders of the drug ring out of trouble in Columbia.

In mid-1977, the group sent Davila a case of disposable diapers to signify "the baby is ready, send the mother [ship loaded with marijuana]."

In April 1978, the indictment charged, Ronald B. Elliott, a former Eastern Air Lines pilot and another of those charged, said he had a plan "to steal an Eastern Airlines Boeing 727-type aircraft, use it to smuggle a load of marijuana into the United States and then ditch the aircraft over the Atlantic Ocean."

In July 1977, Mark S. Phillips, a Fort Lauderdale yacht broker who also was indicted, allegedly walked into the Landmark Bank in Fort Lauderdale and took $223,000 in cash from a suitcase to pay the owner of an 85-foot yacht the group wanted to refit for smuggling. The name of the vessel was changed from "Naughty Girl" to "Presidential." It later ran aground off the Bahamas and was lost to police there with 31,000 pounds of marijuana aboard, despite frantic rescue efforts by the group, the indictment said.

Meinster allegedly told one member of the group the failure cost him and Platshorn $1 million. In fact, the indictment alleges the the organization later switched to planes as a safer way to conduct operations. But on one venture, the plane's engines failed and the pilots were stranded in Colombia.

From late 1977 on, the leaders of the group feared that their operations were under surveillance by law enforcement officials and that one of their members was an informant. At one point, one member was sent with a "bug detector" to search the home of a suspected colleague for government eavesdropping equipment.

On another occasion, in April 1978, one member of the group allegedly was given a revolver and told to hijack a plane and, if necessary, to kill the pilot on a smugging-rescue run to Colombia, the indictment said.

Attorney General Griffin B. Bell praised the co-operative FBI-DEA effort yesterday, saying the case was the largest in the drug trafficking field in his experience.

The investigation, called Banco (Spanish for bank), was started in late 1977 in an effort to trace the flow of cash profits from drug smugglers. DEA spokesman Robert Feldkamp said the use of the RICO statue is new to drug investigations.

"It's the way to go," he said. "We're moving away from the old buy and bust."

Frederick Rody, DEA regional chief in Miami, called the indictment "just the tip of the iceberg."

Among the others charged in the case are a foot doctor, a Tampa seafood importer, a Georgia pilot who also manages a day-care center and other pilots and boat captains.