The defense leveled its attack on the key prosecution witness in the bribery trial of former D.C. Superior Court Judge Robert H. Campbell yesterday, getting him to admit that payments he had identified as bribe money for the judge may have been used instead to pay for his own expenses.

The witness, Robert P. Jenkins, once the No. 3 man at a Bladensburg construction firm, had testified in federal court on Tuesday that he had made 10 to 15 payoffs to Campbell to gain lenient treatment from the judge on traffic tickets issued to his company.

Yesterday, defense lawyer Arnold M. Weiner, who once defended former Maryland Gov. Marvin Mandel, spent the entire day slashing away at Jenkins' testimony. Weiner never directly asked Jenkins whether he was lying when he testified that he made payoffs, usually in $100 bills, to the judge from 1975 to 1977. Instead, the defense lawyer continually confronted Jenkins with numerous contradictory versions of the bribery scheme that he has given federal investigators during more than 13 meetings and 38 hours of talks he had with them before he first took the witness stand last Thursday.

Weiner, aggressively questioning Jenkins in a loud, high-pitched voice, made it clear that he wanted the jury to believe that the government had come up with its own theory for a case against the former judge and then planted it with Jenkins, who has already been convicted of perjury in connection with the Campbell investigation. Weiner portrayed Jenkins as a man who was ready to cooperate with the prosecution in order to keep himself out of jail.

As the day wore on, particularly at moments when it seemed apparent that Weiner's questions had seriously damaged Jenkins' credibility, the former judge sat upright in his chair at the defense table and held his hand to his chin, concealing a small smile. His codefendant, Larry A. Campbell (no relation to the judge), who is represented by Weiner, playfully sparred with another defense lawyer at the midafternoon recess, his spirits obviously buoyed by the points Weiner seemed to score during his cross-examination.

Former Judge Campbell, Larry Campbell, the general manager of Excavation Construction Inc., and the firm itself are on trial in U.S. District Court on charges of conspiracy, bribery and racketeering. The government contends that the former judge dismissed hundreds of thousands of dollars worth of overweight truck tickets for the company, trading his judicial influence for more than $10,000 in cash and favors.

Step by step, Weiner led Jenkins through the government's allegations that he had made 10 payoffs to former Judge Campbell with company money. Ten times Weiner asked Jenkins, "You can't say yes or no whether you made such a payment?" and 10 times Jenkins replied, "That's correct," or "No sir."

Weiner then asked Jenkins about a series of expense account withdrawals he had made, money that the government says he used to make payoffs to the former judge. Weiner compared some of those withdrawals with Jenkins' travel records -- records Jenkins said the government had not shown him -- and Jenkins agreed that the withdrawals could have been for travel expenses and not bribes. Jenkins also acknowledged that another payment he had identified as a bribe was actually a check written to and cashed for Larry Campbell. Jenkins testified further under cross-examination that two other withdrawals he identified as bribe money were in fact used to rent an apartment for himself.