After 17 weeks and more than 1,000 exhibits, the government has failed to prove its conspiracy and bribery case against former D.C. official David E. Rivers and contractor John B. Clyburn, attorneys for the two men argued yesterday.

In five hours of summations in U.S. District Court, the two attorneys mapped out their rebuttal to the government's contention that Rivers and Clyburn steered more than a dozen contracts worth more than $2 million to companies owned by Clyburn or his associates from 1982 to 1987.

Rivers, former director of the D.C. Department of Human Services, and Clyburn, a personal friend of Rivers's and an influential city contractor, sat impassively as their two attorneys put forth defenses that often sounded the same theme.

Rivers's attorney, Francis D. Carter, used his full three hours to sum up his case, often mimicking witnesses and at times mocking the goverment's arguments.

There is no proof, he said, that Rivers and Clyburn were "frothing at the trough of the District of Columbia." His client, said Carter, was a competent administrator whose only failing was that he advocated and supported awarding contracts to minorities.

"There's the watering hole. Go to it," Carter said, paraphrasing Rivers. "I'm going to introduce you to people." Carter concluded: "Criminally corrupt? Not by any means."

Most of the evidence -- including more than 300 secretly recorded tapes -- was obtained by an undercover FBI agent working with a businessman who was unaware of the government's investigation.

During nearly 3 1/2 hours of closing arguments on Thursday, Assistant U.S. Attorney Rhonda Fields asserted that Rivers routinely sidestepped procurement procedures and steered contracts to Clyburn and his associates.

Most of the contracts did not require formal review because they were noncompetitive under the city's rules. That, argued Fields, prevented others from questioning the propriety or cost-efficiency of the awards.

Carter and Thomas Dyson, who represented Clyburn, repeatedly asserted that the government's case never proved that payoffs had been made.

"Look at the government's case and see what is not there," Dyson said. "Many times what you don't see is the most important thing. There's no money, there's no fictitious employees . . . . "

An underlying theme of the trial has been the city's method of awarding contracts. Dyson argued that Clyburn merely used his government contacts. "That's what people in Washington, D.C., do all the time. It's being done right now, as you and I are talking in this courtroom," said Dyson.

Carter's sharpest attacks were directed at the FBI and its undercover agent, R. Leonard Carroll. He painted Carroll as an overzealous agent who, perhaps under pressure from superiors, pursued Rivers even when it was clear the administrator was not going for the bait.

At one point, Carroll tried to interest Rivers in ventures including offshore banks and the air rights over Metro stations. Rivers, said Carter, ignored the offers.

"Where does that go? Nowhere. Absolutely nowhere, ladies and gentlemen," said Carter. "But {the government is} still trying."

On Thursday, U.S. District Judge Joyce Hens Green sequestered the 12 jurors and four alternates after Rivers was mentioned in the drug and perjury trial of Mayor Marion Barry. A witness in that case testified that Rivers was one of several people who used drugs with Barry on one occasion. Rivers has not been charged with any drug crime.

The jurors adjusted to the sequestration with "great zest," Green said from the bench yesterday. The case is to resume Monday with rebuttal by the government.