The federal jury hearing the bribery and conspiracy trial of former D.C. Department of Human Services director David E. Rivers and D.C. contractor John B. Clyburn was ordered sequestered yesterday after Rivers was mentioned in the trial of Mayor Marion Barry as someone who allegedly used cocaine with Barry.

U.S. District Judge Joyce Hens Green, who is presiding over the Rivers-Clyburn trial, said she was isolating the 12-member jury, along with four alternates, because "I have to do everything that I can" to protect against possible taint from the development in the Barry case.

Green said she did not think it would be sufficient to warn the jurors not to watch or read anything about the Barry trial, and that a mistrial in the long-running case might be necessary if the jury were not sequestered.

"I would like the jury to make a decision in this case," Green said. Because the case is nearing its conclusion, the judge said, "it is more and more important that they {the jurors} be free of any possibility of prejudice."

The move to sequester the jury came in the 16th week of the Rivers-Clyburn trial and as Assistant U.S. Attorney Rhonda Fields was midway through her closing argument. Defense closing arguments are expected to be completed today.

Rivers's name surfaced in the Barry trial during defense attorney Robert W. Mance's cross-examination of Carole Bland Jackson, who testified that she had seen Barry use drugs in a Southwest Washington apartment with Hazel Diane "Rasheeda" Moore, Moore's sister, Barry friend and photographer Gaylord Tissueboo and "another gentleman."

When Mance began to question Jackson about the incident, he mentioned Rivers's name as one of the people who allegedly used drugs that night. After a conference with U.S. District Judge Thomas Penfield Jackson at the bench, defense and prosecution lawyers agreed that Rivers's name would not be mentioned again during the Barry trial.

Rivers, who also served as secretary of the District of Columbia, is the highest-ranking city official who has been alleged in court to have used drugs with Barry.

Rivers has not been charged with any drug offense. A search of his home in May 1987 in connection with the bribery charges yielded residue of cocaine and marijuana.

Rivers's attorney, Francis D. Carter, said yesterday he had no comment on the testimony in the Barry trial.

All discussions about the mention of Rivers in the Barry trial took place while the Clyburn-Rivers jurors were out of the courtroom. They were told they were being sequestered at the conclusion of Fields's arguments.

During nearly 3 1/2 hours of summation, Fields methodically detailed how Rivers routinely sidestepped normal District procurement procedures to steer contracts worth as much as $2 million to Clyburn or his friends, mostly through Clyburn's consulting company, first known as Granville Corp. and later called Decision Information Systems Corp.

Most of the contracts were so-called sole-source or noncompetitive contracts that were never submitted to the formal contract review process, Fields said, because that would have raised questions about their propriety and cost efficiency.

In instances when contracts were questioned, Fields told the jurors, Rivers "stacked" the review panels with his cronies or manipulated documents to "cover up" improper payments.

She said Clyburn was so much a part of the contract process that when Rivers's own department members needed to confer with him, they often had to go through Clyburn. But in every case, Fields said, Rivers was careful to keep his name off official documentation so that "Mr. Rivers could be insulated in helping his friend, so he wouldn't be on the point" in any controversy.

Rivers and Clyburn, who testified in their own defense, have said that their actions regarding the suspect contract were the result of "networking" and were informal and proper business practices.

"It is a crime to defraud the District of Columbia by giving away the citizens' money," Fields said. "They were stepping way over that networking line."