BOGOTA, Colombia (AP) _ U.S., Colombian and Ecuadorean naval forces will conduct joint exercises in anti-submarine warfare this week, two days after the second discovery of a submarine believed used to smuggle cocaine.

U.S. forces are sending the submarine USS Seahorse, the destroyer USS Stump and three Coast Guard frigates to take part with Colombian and Ecuadorean warships in Operation Unitas XXXV, which begins Friday in the Pacific off western Colombia, said a Colombian naval officer.

The officer, who spoke on condition of anonymity, said the operation ''has absolutely nothing to do with drug traffickers.'' But she acknowledged that anti-submarine techniques learned during the exercise could later be used against smuggling.

In the past three months, police have found two mini-submarines they suspect were used to smuggle cocaine from Colombia, the source of 80 percent of the world's supply of the drug.

The second sub was discovered Wednesday at a repair shop in the Caribbean coastal city of Barranquilla, 435 miles north of Bogota.

The short-range submarines are apparently used to sneak cocaine from port areas patrolled by security forces to mother ships waiting offshore.

Colombian Defense Minister Fernando Botero said after the first submarine was discovered in September that the Cali cartel, Colombia's biggest cocaine- trafficking network, was developing a fleet of submarines.

Found in Santa Marta, a coastal city 50 miles northeast of Barranquilla, the first ''narcosubmarine'' had a sophisticated communications system and capacity for two crewmembers and three tons of cocaine.

Police said the craft found Wednesday was a cruder version, and that it had probably been used for several years.

The joint exercise will be based for two days at Bahia Malaga, a naval base 230 miles southwest of Bogota, and will then move to Panamanian waters, a Columbian navy communique announced.

The U.S. Embassy had no immediate comment on Operation Unitas, an annual joint exercise that began 35 years ago.

The participating U.S. ships are based in Mayport, Fla.; Norfolk, Va.; and Charleston, S.C., the Colombian naval officer said.