President Carter yesterday nominated D.C. Superior Court Judge John Garrett Penn, widely respected for his blend of judicial temperament and common sense, to fill one of two vacancies in the U.S. District Court here.

Penn, 46, was appointed to Superior Court in 1971 after serving 10 years in the tax division of the Justice Department. If confirmed by the Senate, he will be the fourth black among the 15 full-time federal judges here.

"I'm very pleased, very excited, very delighted," said Penn after being informed of his nomination by the White House yesterday afternoon.

Penn has used his tax experience well on the Superior Court. In 1974 he ruled that the city had unfairly revalued real estate for tax purposes and two years ago he upheld the legality of the District's tax on professionals while ordering the city to refund as much as $7 million because some people had to pay the tax earlier than others.

He once defined judicial temperament as common sense -- "what southerners call mother wit.

"It's a big factor in being a judge. You can take almost every rule of evidence and even if you had very little knowledge of the law you could apply common sense and arrive at a just conclusion," he said.

Although Penn always thought of a judicial appointment as the crowning achievement of a lawyer's career, he was surprised when he was nominated by then president Richard Nixon to Superior Court.

"I always thought of a judgeship as something that would come later, but frankly I found it very hard to turn down," he said in a 1976 interview.

Penn's nomination to the federal bench, filling the seat left vacant by the death of Judge Joseph C. Waddy, leaves President Carter with one more District Court nomination here -- the seat vacated when Howard Corcoran assumed senior judge status a year ago.

That vacancy has been caught up in a controversy ever since the president nominated Carin A. Clauss, the Labor Department's chief legal officer. Her nomination was opposed last year by the American Bar Association, and last week Clauss asked President Carter not to resubmit her name to the Senate.

Carter is expected to nominate another woman to fill that vacancy. Three women were approved along with Penn for the Waddy vacancy by the D.C. Judicial Nominating Commission and they could be named in place of Clauss. The women are all Superior Court judges -- Norma Holloway Johnson, Joyce Hens Green and Sylvia Bacon.