BOGOTA, COLOMBIA -- Dozens of weapons given by the United States to Nicaraguan contra rebels are ending up in the hands of Colombia's violent cocaine cartels, according to Colombian officials, who say they are worried that the flow could increase.

At the same time, intelligence units in Colombia and the United States are investigating reports that a boatload of sophisticated weapons, shipped from Italy and destined for the Medellin drug cartel, arrived in Venezuela and was shipped to Colombia during the last two weeks.

A report issued this month by Interpol in Colombia outlines a new, formal alliance between the Colombian cocaine cartels and criminal organizations in Italy and Spain to provide and distribute cocaine in Europe.

"We think the shipment, if it took place, could be the beginning of arms-for-cocaine deals with the Italian mafias," said a senior intelligence official. "Essentially, this alliance saves the cartels a decade of work setting up distribution systems in Europe and gives them access to people with a long history of obtaining weapons."

In the past, U.S. authorities have acknowledged that about 80 percent of the drug traffickers' weapons came from the United States, and Colombian officials are worried and angered by the flow of arms from the contras, which some blame indirectly on the United States.

"Right now, we are not talking huge amounts of weapons found. We are talking about dozens, not hundreds, but it is growing and it is worrying," said a senior Colombian official who monitors the drug war. "Contra weapons are a new source of supply for the cocaine cartels."

The official, who has access to intelligence reports, said the contras appeared to be selling their weapons on the arms market in Central America. These include U.S.-made M67 fragmentation grenades and Soviet-made AK-47 assault rifles and RPG-7 grenade launchers that the United States gave to the contras so they could use ammunition and spare parts from arms captured from Soviet-backed Sandinista troops. The weapons were being purchased by the cocaine barons because they could pay premium prices, he said.

A new intelligence report by the government of Costa Rica, made public by Aportes magazine in San Jose, said the contras, in demobilizing on June 25, turned in only half of their weapons to United Nations observers and are selling the rest to Colombian drug traffickers and others.

"Persons tied to drug trafficking have acquired all types of light arms and explosives, from AK-47s to land mines, that were given by the United States to the Nicaraguan Resistance {contras}," the report said. Its authenticity was confirmed here.

The report said the contras turned in 62 Redeye portable antiaircraft missiles "but according to the inventories given by the government of the United States to the United Nations, half of the sophisticated arms are missing."

"The transfer of arms takes place along the San Juan River {the border between Nicaragua and Costa Rica}, where former members of the Nicaraguan Resistance sell their weapons to the highest bidder," the Costa Rican report said. "The arms are transported to Colombia aboard small airplanes, using the same routes and clandestine airstrips used to ship cocaine to the United States."

Reports of increased arms shipments come at a time when Colombia is experiencing a sharp decline in drug-related terrorism.

Officials here say the Medellin cartel has been badly hit by government forces in recent months, when several of the cartel's top officials have been killed or arrested and cartel leader Pablo Escobar has been kept on the run. The officials say the cartel may be keeping a low profile while it rearms to strike back.

"No one really knows what Pablo Escobar is really thinking," said a senior Colombian law enforcement officer. "Everything indicates he is badly hurt, and he should give up. But in the past, he has always wanted revenge, he always wants to strike back. He is like a wounded tiger, more dangerous now that he is cornered."