Jury selection began yesterday under heavy security in U.S. District Court here for a panel of jurors that will be sequestered throughout the trial of Marcos Cadavid, an accused Colombian cocaine wholesaler.

U.S. District Judge Thomas F. Hogan said sequestering of the jury was necessary because of publicity and "other surrounding circumstances."

The extradition of Cadavid two months ago from Colombia under a new treaty aimed at cracking down on international drug dealing has drawn threats of violent retaliation from South American cocaine kingpins, law enforcement officials said.

Cadavid, 43, is charged with conspiracy to import and distribute cocaine from 1976 to the end of 1982.

The jury selection process is expected to be completed today. Hogan said the trial likely will last about a week.

Security was in place yesterday in the federal courthouse. Stairwells and some entrances were sealed and special restrictions on parking adjacent to the building were in effect.

Police carrying automatic weapons patrolled the courthouse roof shortly before Cadavid was driven away late in the day.

Law enforcement officials have said the security precautions followed general threats of revenge from Colombian drug dealers, who are bent on damaging the new era of cooperation between the United States and Colombia.

"We do not have specific threats against" Cadavid, said a Drug Enforcement Administration intelligence officer.

The DEA officer said Colombian government officials are watching the Cadavid proceedings closely, however, to see whether extradited defendants can be processed without incident through the U.S. criminal justice system and whether the proceedings will end in convictions.