Traffic was halted and onlookers gawked yesterday as a black limousine escorted by police motorcycles and heavily armed guards sped from an underground garage at the U.S. District Court building in Washington.

The caravan, with flashing red lights and screaming sirens usually used for high government officials and visiting heads of state, carried a 43-year-old Colombian citizen who, these days, is considered a Very Important Person by the Justice Department.

He is Marcos Cadavid -- not a dignitary, but an accused South American cocaine kingpin. Cadavid was extradited from Colombia last month to stand trial here March 11. His extradition pleased U.S. law enforcement officials but angered major Latin drug dealers.

The extradition is part of a general, U.S.-sponsored crackdown on the international drug trade from the Southern Hemisphere that reportedly has brought threats of retaliation from big-time South American cocaine exporters.

The U.S. attorney's office here refuses to discuss details of the security surrounding Cadavid. A law enforcement source said, however, that U.S. intelligence has reported that hitmen have been dispatched to this country in the wake of the stepped-up drug enforcement effort.

Whether cocaine traders hope to assassinate a key drug defendant such as Cadavid or inflict violence on U.S. law enforcement or court personnel is unclear, according to the source.

But such an attack presumably would serve as a warning to defendants who might otherwise be tempted to cooperate with federal prosecutors.

Security arrangements surrounding court appearances here by Cadavid are said to be extraordinary and perhaps unprecedented, according to courthouse regulars.

On at least two occasions, Cadavid has been whisked to court for pretrial hearings, transported in a limousine with smoked-glass windows and escorted by U.S. Park Police motorcycles. During one of his visits in mid-January, police with automatic weapons were visible on the courthouse roof.

Yesterday, security measures inside the courtroom of District Judge Thomas F. Hogan, who has custody of the Cadavid case, included about a dozen armed U.S. marshals, some of whom sat facing spectators, with their backs to the courtroom proceedings.

Federal prosecutors have charged that Cadavid and others smuggled hundreds of kilograms of cocaine into the Miami area through a food distribution warehouse used as a front. Much of the cocaine allegedly was purchased and distributed through a Washington-based network of drug dealers, according to prosecution testimony.