At least one person intimately involved in the drug conspiracy trial of Mayor Marion Barry finds the prospect "exhilarating": the judge.

Thomas Penfield Jackson is a federal judge by title, but at heart he is a litigator -- someone who doesn't enjoy the abstractions of law as much as the thrust and parry of a hotly contested trial. Which is what he expects in the Barry trial.

"This is going to be a well-tried case," he said one day last week, sitting in his chambers and tamping his ever-present pipe. "Both sides in this are good. Really good."

At 53, this third-generation Washingtonian has been on the bench for eight years, the first Reagan appointee to the U.S. District Court here.

Before that, he was a partner in the law firm of Jackson & Campbell, in a practice devoted to civil cases in general and medical malpractice cases in particular. The "Jackson" in the title refers to his father, Thomas Searing Jackson. Federal judges are forbidden to keep their names in a law firm's masthead.

While he has presided over a number of newsworthy cases, including the 1988 trial of former White House chief of staff Michael K. Deaver, Jackson has maintained a low profile in the courthouse here.

He takes pains to keep his personal and professional lives separate. His re'sume' and entry in the Judicial Staff Directory list dozens of cases he has decided -- but nothing about his family. The judge said he is married and has two daughters.

It is fitting that Jackson will be hearing the Barry case in the same courtroom that housed the Watergate trials, because the Watergate scandal probably helped propel him onto the bench. It was Jackson & Campbell that represented CREEP, the Committee to Re-Elect the President -- President Nixon's 1972 reelection campaign group.

After some of the most damaging Watergate revelations, Jackson's firm represented CREEP when it was sued by the Democratic National Committee and Common Cause, both of which sought the names of campaign contributors. Both cases ended in settlement.

Later, the firm defended one of its partners, Kenneth Parkinson, when he was indicted in 1974 on a conspiracy charge in connection with work for CREEP. Parkinson was acquitted.

"Ultimately," Jackson said, "we decided with a good deal of trepidation, that {Parkinson} was deserving of our loyalty. But it was a long year."

When, eight years later, Jackson's name came up for consideration for a federal judgeship, he said, "I'm inclined to think some people remembered me favorably from the Watergate litigation."

Jackson's former law clerks speak of his ability to use the skills that make a good litigator -- in Jackson's words, "a lawyer who knows the issues, who calls appropriate witnesses . . . and who knows when to sit down."

He also recounts some of his courtroom victories. There was the cross-examination of an obstetrician in a malpractice case. Jackson, representing the doctor, spent a torturous weekend figuring out how to approach a witness who he was convinced was lying. That Monday, in court, Jackson stood when the judge said it was time to question the witness.

"Your honor," he said scornfully, "I have no questions of this witness." His putdown was so well-delivered that it may have been a turning point in the case. The lawyers on the other side went crazy. Jackson's client won.

It is courtroom skills, he believes, more than a theoretical grasp of the issues, that determine whether justice is done.

"When you get good lawyers on both sides . . . and a judge willing to remain a judge, and the case is significant enough to call forth the best efforts of those lawyers, you come about as close to true justice as humans can produce," Jackson said.

Jackson said that the Barry case may present some procedural problems, but the judge said he was downright troubled by one issue: the prospect that racial issues will be interjected into the case.

"I'm going to do everything in my power to keep that out of the case," he said. "It should have absolutely no relevance."

Otherwise, he said, he's looking forward to the trial. He grins. "Oh, yes."