Nearly three months into the conspiracy trial of former Department of Human Services director David E. Rivers and D.C. contractor John B. Clyburn, Rivers yesterday got his first chance to tell his side of the story in federal court.

In an afternoon of questioning by his attorney, Francis Carter, Rivers offered his version of his dealings with an undercover FBI agent who provided much of the evidence against him and Clyburn.

He also told of how a fledgling company named JMC Inc. came to flourish under his guidance. A key portion of the government's early evidence suggested that certain firms connected to Rivers or Clyburn were given Human Services contracts whether or not they were capable of doing the work.

Rivers is expected to continue his testimony today in the courtroom of U.S. District Judge Joyce Hens Green. It was unclear whether Clyburn was going to take the stand in his own defense.

Rivers and Clyburn are charged with conspiring to steer more than $2 million in Department of Human Services contracts to companies owned by Clyburn or his friends. But dogging the prosecutors from the start has been the issue of how to differentiate between illegal conspiracy and old-fashioned networking.

In his testimony yesterday, Rivers presented his dealings with Clyburn as the latter.

Carter led his client through a recitation of the outside pressures that affected how he did his job during his 3 1/2 years as head of the department, from 1983 to 1986.

From the beginning, Rivers said, he was forced to work under the constraints of two federal court decrees, one mandating the release of mental patients at St. Elizabeths Hospital and one ordering the District to find residential homes for patients at the District's home for the mentally retarded, Forest Haven.

In addition, he said, the District's youth detention facilities, Oak Hill and Cedar Knoll, were being operated under the strictures of a D.C. Superior Court consent decree, and his department was faced with complying with Initiative 17, the District law mandating that housing be provided for all homeless people.

Rivers said the pressure to find homes in the community for St. Elizabeths patients was one of the reasons he gave considerable leeway to JMC Inc., a new and untested company that in February 1986 won a $216,000 contract to provide "transitional" beds for such patients.

The contract ended up being expensive for the department -- eventually costing $213,000 for three months of operation, when its original budget called for it to operate for nine months for $216,000 -- but Rivers testified yesterday that he felt the expense was worth it.

"I was under heat at that time for not having the proper facilities" for mental-health outpatients, Rivers said. "Nobody wanted a mentally retarded person or a mentally ill person in their neighborhood."

Rivers added that because JMC was a minority company -- it was owned by Carla Mumby, a friend of Clyburn's -- he thought there was another reason to encourage it to fulfill the contract: encouraging minority business enterprise.

"I thought it would be sensible to extend the contract, so I did," he said.

Carter's next question referred to FBI wiretap tapes of numerous phone calls placed by Clyburn to Rivers to intercede for JMC. Why, Carter asked, did Clyburn have any business talking to Rivers about it?

"That was sort of normal," Rivers replied. He added that he got similar phone calls every day from friends, community groups and even D.C. Council members.

Carter then directed Rivers to talk about his dealings with Detroit businessman Warren Barge and Len Carey -- the latter a pseudonym for FBI undercover agent Leonard Carroll. Barge, in unwitting cooperation with Carroll, formed a minority business company in 1986 called B&C Management Consultants, which immediately set about trying to win some District contracts.

Its first major success came when it won a $24,995 contract to do an energy audit at Forest Haven. That came shortly after a meeting among Rivers, Barge and Carroll, in which Barge and Carroll promised to help underwrite a fund-raiser planned for Mayor Marion Barry in Atlanta.

According to testimony earlier in the case by Carroll, who secretly recorded the meeting, the Forest Haven contract was in direct exchange for their promise to bankroll the Barry fund-raiser.

"Y'all just do this, it's done right now," Rivers was quoted as saying in transcripts of the coversation. But yesterday, Rivers disputed Carroll's interpretation.

"My testimony is that I was simply giving them {Barge and Carroll} invitations {to the fund-raiser}, and that had nothing to do with any quid pro quo," Rivers said.