David E. Rivers, the former head of the District's largest government agency, was acquitted yesterday of bribery and conspiracy charges in what prosecutors alleged was a scheme to manipulate the city contracting process for his own benefit.

The fate of Rivers's codefendant -- D.C. contractor John B. Clyburn, who also is charged with conspiracy and bribery -- remained unknown last night. The federal court jury sent out a note at 6 p.m. saying it had reached a verdict only on Rivers and indicating it was still considering the charges against Clyburn.

U.S. District Judge Joyce Hens Green took the partial verdict and told the jurors, who began their deliberations late Monday, to return today to continue their work.

A beaming Rivers appeared so overcome with emotion that he could barely speak when friends and reporters crushed in on him outside the courtroom. "I feel great," he said moments later. "I'm not guilty. I said I was not guilty. They found me not guilty."

The Rivers trial at one point was touched by developments in the drug and perjury trial of D.C. Mayor Marion Barry. After testimony in the Barry case that Rivers and the mayor had used cocaine together, the jury in the Rivers trial was sequestered. Rivers has not been charged with any drug violations.

Rivers declined yesterday to answer questions about the 16-week trial or the elaborate 17-month undercover operation that led to his indictment in 1989.

Rivers's attorney, Francis D. Carter, said, "We are glad that 12 citizens in the city paid attention to the evidence . . . . I'll leave the analysis {of the government's investigation} to others."

Clyburn, who heartily shook the hand of his codefendant and longtime friend after the verdict, said he was optimistic about his own case. "It's a great verdict," he said.

A spokesman for U.S. Attorney Jay B. Stephens said he would have no comment

until the jury has completed its deliberations.

In a statement issued by his press secretary last night, Barry said, "I'm delighted that justice has been rendered and that the people, i.e. the jury, rejected the overreaching, overzealous U.S. government and U.S. attorney's efforts to discredit the Barry administration and ruin people's lives and reputations. Thank God."

The trial gave the public a detailed look at allegations that have plagued the Barry administration for years: namely, that the contracting process was corrupt. In the case of Rivers, who headed the D.C. Department of Human Services from 1983 to 1986, the jury found that it was not.

The government accused Rivers and Clyburn of working together over a four-year period to manipulate the city contracting process for their own benefit at the Department of Human Services.

It was a scheme, the government charged, that involved stacking contract evaluation panels, revealing confidential information, corrupting other D.C. officials and ultimately trying to cover up misdeeds.

One source familiar with the investigation said the case had been a complicated one to present, with no "smoking gun for jurors to latch onto."

As is often true in cases of alleged conspiracy, jurors had to put together a long string of subtle evidence, the source said.

From its start in 1986, the government's elaborate undercover operation involved the creation of a sham company that sought contracts from the District and months of wiretaps and secret recordings. Prosecutors presented nearly 1,000 exhibits, including 300 taped conversations, in the four-month trial.

In his closing arguments, defense attorney Carter hammered hard at the FBI operation, portraying undercover agent R. Leonard Carroll as an overzealous agent who, perhaps under pressure from superiors, pursued Rivers even when it was clear Rivers was not going for the bait.

Rivers denied the charges, and Carter told jurors as the trial opened that "at no time {did} my client take a penny from the FBI sham man," referring to Carroll.

Rivers and Clyburn were charged with steering more than $2 million in contracts to companies owned by Clyburn and his friends and unsuccessfully trying to channel a contract worth millions more to a Clyburn ally.

The taxpayers, the prosecutors charged, were the losers in the scheme, as city contracts went to a private circle of friends instead of the most qualified bidders.

Rivers's reward, the prosecutors charged, was the promise of future cash benefits from the owner of one of the companies he helped -- a company that turned out to be an FBI front run by Carroll.

For Clyburn, the goal was increased business for his firm and those of his friends, the government charged.

The defense portrayed the actions of the two men in a vastly different light, suggesting that Rivers was merely trying to aid minority contractors.

Clyburn, with contacts throughout the city government, was merely doing old-fashioned networking and trying to give other black contractors a shot at business, his attorney said.

A key element of the case was the government's assertion, spelled out in tapes of Rivers's conversations with undercover agent Carroll, that Rivers planned to parlay his clout as a high-ranking city official into future cash benefits when he left government.

In several conversations, Carroll discussed his plans to put aside money for Rivers in a variety of investments. The prosecution asserted that Rivers heartily agreed to one of those plans.

But Carter offered a different interpretation of those tapes, saying that Rivers never took a cent from the agent -- an assertion the government did not dispute -- and that he never planned to take any money in the future.

Carter suggested that Rivers was merely allowing Carroll to ramble on about his schemes.

Yesterday's verdict came after an unusual series of events. The jury sent a note to Green at lunchtime, indicating that it had reached a verdict on one of the defendants.

The prosecution and defense met with Green and agreed that if jurors had not reached a verdict on both defendants by 6 p.m., Green would take the verdict on Rivers and send them back to work today.

That plan, the judge said, would "ensure the continued integrity of the process."

The jury had deliberated about 12 hours before reaching yesterday's verdict.

When Green called for the verdict, the 46-year-old Rivers stood stoically, with his hands folded, facing them. Four times, to four separate counts -- one of conspiracy and three of bribery -- the foreman said "not guilty." Rivers barely moved.

Later, outside the courthouse, he said that the charges would likely "continue to have an impact {on my life}, but hopefully I can get around that."

"Now I can get my life back in order," said Rivers, who now works as a special assistant to the director of the D.C. Department of Public Works.

"I'm going to get away, take a vacation and reflect. I'm just glad it's over," he said.