Colombian authorities today extradited a suspected Venezuelan drug trafficker who could be the key to Washington's attempt to try Colombia's undisputed cocaine kings, the Rodriguez Orejuela brothers, in a U.S. court.

Fernando Jose Flores, 38, nicknamed the Fat Man, is the second alleged drug smuggler extradited this week. He is accused of shipping more than 3 1/2 tons of cocaine to Florida, packed in concrete fence posts.

He was reputedly a crony of the Rodriguez Orejuelas, who have been serving time in a Bogota prison since their capture in mid-1995.

Flores has said he fears U.S. officials will force him to give evidence against the Rodriguezes, former kingpins of the notorious Cali drug mob who were once blamed for 80 percent of the world's cocaine traffic.

Colombia banned the extradition of Colombian citizens in 1991 after Pablo Escobar, then capo of the Medellin cartel, waged a bloody campaign of bombings, murders and kidnappings. Escobar was killed in 1993 during a shootout with police on a Medellin rooftop.

Under intense U.S. pressure, Colombia's congress lifted the ban in December 1997, but the measure only covers crimes committed after that date.

No Colombian had been sent abroad for trial since 1990 until Sunday's extradition of suspected heroin trafficker Jaime Orlando Lara, 30.

The extradition of foreign nationals was never suspended. But after Flores's capture in August 1998, he argued that he was a Colombian citizen and his crimes were committed before the resumption of the extradition treaty with the United States.

Flores was bundled aboard a U.S. Drug Enforcement Administration jet at a Bogota police airport after extensive medical checks. Just 5 feet 6 inches tall but weighing 308 pounds, Flores has heart problems.

Under the gaze of scores of heavily armed police officers, he crossed the runway with tubes in his nose from a small oxygen canister to help him breathe. He was not handcuffed, but police officers gripped his arms.

Neither Flores nor police chiefs made a statement at the airport. But in an interview published this week by the magazine Semana, Flores voiced fears about his imminent extradition.

"With threats, psychological torture. . . . I will sign whatever [U.S. officials] put in front of me so that they get what they want--the extradition of the Rodriguezes," he said.

Colombia rejected an extradition request for the Rodriguezes in mid-1996. U.S. authorities, however, say the two men have continued to run their criminal empire from behind bars and could be liable for extradition for acts committed after December 1997.

Both men were convicted of drug trafficking and sentenced to terms that could allow them to be freed from Bogota's top-security La Picota prison in less than 10 years. If ever tried in the United States, the Rodriguezes could expect much stiffer sentences, possibly even multiple life terms.

Colombian authorities have warned that the resumption of extradition ties with the United States could spark a violent backlash by the country's drug mobs.

Two weeks ago, seven people were killed by a car bomb in northern Bogota in an attack that police blamed on either drug traffickers or Marxist guerrillas.