In an undercover operation lasting 22 months and code-named "Grouper," the Drug Enforcement Administration broke up 14 marijuana-smuggling rings in four states that accounted for as much as 40 percent of the marijuana coming into the United States every year, the agency said yesterday.

By mid-afternoon, the DEA said that 122 people had been arrested in Florida, Georgia and Louisiana on drug-smuggling and conspiracy charges. Bail in one case was set at $21 million and in two others at $20 million apiece.

Bail for seven persons described as kingpins of the 14 smuggling rings exceeded $100 million. The DEA said Grouper resulted in the seizure of more than 1.1 million pounds of marijuana, whose street value was more than $1 billion.

"This was the single largest enforcement activity against marijuana since I've been here," said Peter B. Bensinger, now in his sixth year as DEA administrator. "The heads of every one of these 14 smuggling rings have been indicted."

One of the most sought-after members of the 14 rings was found murdered yesterday, and still at large were 31 of the 155 ring members indicted by federal grand juries in Florida, Georgia, Louisiana and Texas, where nine undercover DEA agents worked since May 1979 investigation marijuana smuggling.

Bensinger described Grouper as an operation whose origins went back 2 1/2 years, when nine DEA undercover agents began selling their services as marijuana "off-loaders" promising security and efficiency on the job. The operation caught on 22 months ago, when the DEA gave the nine agents the green light to continue posing as marijuana off-loaders going from job to job like gypsies.

The agents unloaded six shipments of marijuana before acting as DEA agents. They then began to signal their superiors what ships were leaving Columbia with marijuana and where they could be stopped on the high seas. No fewer than 24 ships carrying almost 1 million pounds of marijuana were seized at sea by the Coast Guard in the last 18 months following tips from the Grouper agent team.

Seizures of marijuana also were made onshore after the drug had been landed, but they were rare because they could have exposed the roles of the nine DEA agents. One such seizure took place in Louisiana, where police conducting a house-to-house search pretending to look for a lost child confiscated a cache of marijuana but let the ring members flee.

"For nine agents to operate undercover like this for 22 months was remarkable," Bensinger said. "In that time, they conducted 400 undercover meetings with members of these smuggling rings, which we estimate were responsible for between 30 and 40 percent of the marijuana being smuggled into the country."

Bensinger said the undercover agents used the tape recorders and videotape machines, whose evidence is to be introduced in court against the defendants the way similar evidence was in the FBI's Abscam undercover operation.

"The tapes show that the defendants clearly demonstrate their intent to subvert the law," Bensinger said. "They will demonstrate conspiracies to distribute drugs in the United States. We think this is an extraordinary example of the success of a unique undercover operation.We hope there will be more."