Last November, Mr. Wilkes was described as “co-conspirator No. 1” in a plea agreement signed by Representative Randy Cunningham, a California Republican on the House Appropriations Committee. In the plea deal, Mr. Cunningham admitted accepting more than $2.4 million in cash and gifts from Mr. Wilkes and other contractors. Another defense contractor, Mitchell J. Wade, pleaded guilty to paying some of the bribes.

Mr. Wilkes could also figure in a related federal investigation into the House Appropriations Committee. The inquiry has focused on ties between Mr. Lowery, who left Congress and became a lobbyist, and Representative Jerry Lewis, a California Republican who is the chairman of the committee and the former chairman of its Defense Subcommittee.

Speaking publicly for the first time since Mr. Cunningham’s plea agreement, Mr. Wilkes said in recent interviews that he had done nothing wrong and did not believe that Mr. Lewis and Mr. Lowery had broken the law. Mr. Wilkes, who has not been charged in the Cunningham case, has refused prosecutors’ appeals to plead guilty.

But Mr. Wilkes acknowledged that he was a willing participant in what he characterized as a “cutthroat” system in which campaign contributions were a prerequisite for federal contracts. “I attempted to get help and advice from people who could show me the way to do it right,” Mr. Wilkes said. “I played by their rules, and I played to win.”

Mr. Wilkes said he was speaking now to rebut false assertions about him by prosecutors and the news media. While it is unknown whether his account is complete and it is impossible to verify his recollections of certain conversations, many aspects of his story were confirmed by federal records, other documents and interviews with people involved in the events he described.