On Sept. 17, 1977, U.S. authorities picked up a 30-year-old Colombian among the crew of the Juliana I off the coast of Cape May, N.J. Their cargo: 25 tons of marijuana.

On Aug. 1 of the following year, they apprehended a 31-year-old Colombian and his fellow crewmen with 30 tons of marijuana on the Los Dos Amigos, 85 miles northwest of Cuba and headed for the Gulf of Mexico.

Then on Dec. 8, 1978 - in the gulf - they nabbed a 31-year-old Colombian with 20 tons of marijuana on the San Nicolas.

Each time, it was the same man.

Because he had been apprehended in international waters, he could not be charged. Instead, he was merely deported back to Colombia - with a plane ticket paid for by the U.S. government.

Another Colombian crewman was apprehended and deported twice in a 48-day period last year after he was found on ships whose marijuana hauls totaled nearly 44 tons. Less than a year before, he had been seized with other crewmen and 12 tons.

A third Colombian seafarer - they are recruited from that country's northern coastal towns - was arrested on three ships between Dec. 3, 1977, and Jan. 16 of this year. The marijuana - 47 tons.

Authorities say there is no reason to believe these were the only trips the three men had attempted.

While such repeaters frustrate law enforcers, the three men, as well as 60 others arrested time and again on mother ships, have provided new insight into the Colombian-based marijuana export industry. The conclusion: No more than a handful of gangs in Colombia - four or five - essentially control the highly lucrative marijuana traffic to the United States.

The 63 men were found among 574 crewmen aboard 51 "mother ships" - vessels whose large cargoes are transferred to smaller smuggling boats - seized over a four-year period. Examining the 63 men's associations - tracking who had been on which ship when - leads a U.S. Customs analyst to conclude that 49 of the 51 ships belonged to just four or five Colombian organizations.

Moreover, he found, there appear to be highly skilled ships' masters and engineers, trusted by the organizations, who put together the crews.

"It's almost like a longshoreman's union hiring hall," said the analyst, Jack Gregory of the maritime surveillance unit at the El Paso Intelligence Center.

So low is the risk, said Gregory, that one man left Colombia on a mother ship less than a week after he had been deported from the United States.

And the profits to the suppliers are great. Shipments seized so far this year have ranged from 5 1/2 tons to 33 tons. But the record belongs to the Heidi, 150 feet of coastal freighter sitting off Jacksonville, with 112 tons of marijuana - 3,584,000 one-ounce Baggies.

These mother ships - coastal freighters, shrimpers and fishing boats typically weather beaten but sometimes almost new - bring their cargoes from the Guajira peninsula in Colombia mostly to sites off Miami and South Florida.

Such large-scale shipments have made the region a national capital for the importation of marijuana - as well as cocaine and methaqualone.

In some cases, reports Coast Guard Cmdr. George Martin, the ehief of intelligence and law enforcement here, drug runners have bought entire islands in the Caribbean as "stash islands" for temporary storage of drugs destined for the United States.

But increased enforcement and crackdowns on mother ship operations have, by some accounts, forced importers to use more airplanes or move west from Florida.

Last week in Houston, for example, five men were arrested with 11 tons of Colombian marijuana that had apparently entered through that port. Three of the men gave police home addresses in Miami.

At least five Colombian organizations in Miami dominate large-scale marijuana trafficking, and an investigator says there appear to be family links between the Miami organizations and the handful of groups in Colombia.

Using sophisticated radio navigation, the mother ships wait in international waters for the importers to come and get their marijuana. Officials here say this puts the risk on the buyers as they bring it to shore. There is, for all practical purposes, no law against having a load of marijuana on the high seas.

But if the marijuana is destined for the United States, it and the ship can be seized. The crew, most times, goes free. Gregory in El Paso reports that at least one crewman apprehended three times in his study has been rearrested twice more in the past few months.

"They don't get nasty," Martin says, "because they don't have to." Nothing happens to them.

So halting smugglers is an endless task, Martin says, one that probably wouldn't be ended by massing ships, planes and troops in South Florida.

In a May indictment, U.S. prosecutors alleged that Miami's Black Tuna gang - named after the codeword of their Colombian supplier - monitored secret and sensitive Drug Enforcement Administration radio channels while transporting marijuana from the mother ships to shore.

The group allegedly maintained a sophisticated communications van and also had a security force called "Chip's Army," after its leader.

Other drug operations have been successful with less effort than stealing secret radio information and equipping vans with monitoring equipment.

Cmdr. Martin remembers the day guardsmen preparing to board a mother ship heard it transmit a message that sounded meaningless. Almost immediately a distress call crackled on the radio: Lost engine...drifting a shore...need help...100 miles away.

The cutter crew responded to that summons. They found the distant ship, Martin said, "but it had "regained" power. And it neither needed nor wanted any assistance."

And the mother ship was long gone. CAPTION: Picture, A typical marijuana mother ship is loaded in Colombia; Picture 2, The Heidi, seized off Jacksonville, Fla., yielded a record 112 tons in burlap bags. Drug Enforcement Administration Photos; Map, shows favored routes for smuggling drugs to United States from Colombia. By Dave Cook - The Washington Post