He walks into the courtroom slowly. Spectators sometimes have to strain to hear his voice. But in 16 years as a U.S. District Court judge, Barrington D. Parker has handled some of Washington's most celebrated cases -- and relished them.

"I had no way of dreaming the sort of things that would come across my life," said Parker, who turns 70 today and plans to take semiretired senior status next month.

"When I was growing up, you know, Washington was quite a different city," he said. "I've seen segregation and discrimination in its rawest terms. It lives with you."

Over the past decade the defendants in Parker's courtroom have included John W. Hinckley Jr., the presidential assailant found not guilty by reason of insanity; Richard Helms, the former Central Intelligence Agency director accused of lying to a Senate committee; former representative Otto E. Passman (D-La.), charged with accepting a bribe from a South Korean businessman, and two Cuban exiles and a Chilean security agent accused of murdering Orlando Letelier, a former Chilean ambassador.

In 1979, Parker blocked President Carter from issuing wage and price guidelines and in 1982 he ruled invalid a congressional amendment that barred Communists from job training programs.

In one of the rulings he says he is most proud of, Parker refused to accept a plea bargain in 1979 worked out between the Justice Department and Westinghouse Electric Co. in a foreign bribery case until attorneys revealed the name of the official -- a deputy Egyptian prime minister -- who received the bribes.

"I certainly don't perceive myself as just calling strikes and balls," Parker once said in describing how he presides in court. "The lawyers want to try their own cases. But a judge shouldn't just sit there when a lot of questions come to mind," he explained last week. "If there is something I want to find out, I ask about it."

This aggressive approach and his passion for courtroom decorum have gained Parker a reputation as a crusty, highly independent and sometimes irascible judge. An article several years ago in the American Trial Lawyer magazine described him as "the most cantankerous" federal judge in Washington.

But even some of the lawyers who have felt the sting of his criticism praise Parker for his open-mindedness.

"He's a no-nonsense judge who makes sure you know who's in charge in his courtroom," said a lawyer who has practiced before Parker for many years. "But if you can point out where he made a mistake or overlooked a point of law, he's amenable to changing his mind."

Still, the stories are legion about Parker's persnicketiness in the courtroom. He will not tolerate people draping topcoats over seats or lawyers placing briefcases on the counsel tables. Once Parker criticized a lawyer from New York for appearing in a very loud suit. According to another attorney, Parker upbraided a lawyer so often for saying "okay" instead of "yes" that just before she came into his courtroom she wrote "O.K." on her hand in pen as a warning not to utter the offending word.

Many lawyers complain that Parker pushes them too hard to file papers quickly or to wind up their arguments. But he gets his work done quickly too.

Ten years ago Parker was struck by a car while crossing Connecticut Avenue NW to buy a pack of cigarettes. He lost his left leg as a result and walks on metal crutches. He said he has not smoked since, but he still drives to work from his home in the District's Forest Hills neighborhood.

Born in Rosslyn, Parker is the son of George A. Parker, who started as a bricklayer and mailman and became a part-time preacher and lawyer. George Parker was the founder and dean of the Robert H. Terrell School of Law, a night law school for blacks that closed in the 1950s.

Judge Parker taught there himself and practiced law with his father for more than 20 years, first on U Street and later at Sixth Street NW.

He moved to the District before he started school, and he grew up at 24th and M streets NW. In 1932 he graduated from Dunbar High School, where he met his wife, Marjorie Holloman Parker, who once served on the old appointed City Council and was chairman of the board of the University of the District of Columbia.

The Parkers have two children, Jason, a Chinese scholar who is a staff director for the Council of Learned Societies, and Barrington Jr., a New York City lawyer.

Parker went to Lincoln University, then earned a master's degree in economics from the University of Pennsylvania. He worked briefly as a government economist and taught economics at Dillard University in New Orleans before going to law school at the University of Chicago.

While he was in private practice here, Parker was the president of the D.C. Federation of Civic Associations, a member of the D.C. Human Relations Council and an active Republican. In 1964 he bucked the party by refusing to support Barry Goldwater for president.

Parker was appointed a federal judge by President Nixon, but he said his Republican affiliation now is "very loose cloth." The challenge to affirmative action plans that is being mounted by the Reagan administration, Parker said, is "an attempt to turn back the clock."

Despite his strictness in court, friends say Parker is a genial raconteur off the bench and takes a warm interest in his staff and their families. Even in court, he often asks defendants and witnesses if they are married and where they went to school. "I want to know something about the people I'm dealing with."

As a senior judge Parker will continue to serve with full pay but can cut back his case load.