Defense lawyers yesterday used a prosecution witness to continue their attack on the credibility of Robert P. Jenkins, the man the government says made more than $10,000 in bribe payments to former D.C. Superior Court judge Robert H. Campbell.

Excavation Construction Inc. President John W. Lyon testified in federal court yesterday that Jenkins, the government's key witness against Campbell, was the "primary offender" of company rules about documented expense account withdrawals during the time the bribes were allegedly paid.

Lyon told a U.S. District Court jury that Jenkins repeatedly signed checks off company accounts from 1975 to 1977 but failed to explain how he spent the money. The government contends that the bribe payments from the firm to Campbell were made during those years.

Lyon was called to the witness stand as a prosecution witness to testify about the corporate structure of Excavation Construction Inc., which he built into a multi-million-dollar operation along with the firm's general manager Larry A. Campbell (no relation to the judge).

The former judge, Larry Campbell and Excavation Construction are all on trial for conspiracy, racketeering and bribery. The government contends that Judge Campbell dismissed hundreds of thousands of dollars of traffic fines for the company in exchange for cash and gifts.

Lyon said that Jenkins, who was once the corporate secretary, frequently entertained and traveled on company business in an effort to attract new business to the firm. In that role, Lyon said, Jenkins had ready access to an assortment of company luxuries, including a company-owned boat docked in the Bahamas, resort property in Ocean City, Md., and a suite at the Capital Centre.

Lyon said that although Jenkins frequently failed to document his expenditures, he had no reason to believe that the money was used for anything other than legitimate corporate expenses.

One defense attorney, Arnold M. Weiner, said in his opening statement that the defense would show that Jenkins kept the money that they government said he used to pay bribes and used it in part to support an illicit love affair.

Jenkins, who left his job with the construction company last fall, was convicted in federal court in December 1979 for giving false testimony to the grand jury investigating the Campbell case.

In other testimony yesterday, two former Excavation Construction Inc. Employes testified that they and a third man moved the former judge's household furnishings from one house to another in August 1975, while they were on company time and at the direction of their supervisor. One of the men, Jesse Franklin, told the jury that the former judge gave them $60 to split among them at the end of the day.