Samuel R. Pierce Jr., the only black named so far to President-elect Ronald Reagan's Cabinet and the man tapped to run the sprawling Department of Housing and Urban Development, is a senior partner in one of the nation's most prominent labor law firms and a member of the boards of a half dozen of America's leading corporations.

Pierce, 58, a native New Yorker and lifelong Republican, served as general counsel for the Treasury Department during the Nixon administration.

Although he is not a national figure, he is widely praised and admired in legal, financial and civil rights circles where he is known as a smooth lawyer with an impressive mind and blue-chip credentials.

His resume is something of a catalogue of breakthroughs for blacks, dating back to the 1940s when the tall, solidly built Pierce was star halfback and leading scorer on Cornell University's football team -- and a member of Phi Beta Kappa.

Pierce was the first black to become partner in a major New York law firm, first to serve on the board of directors of two major U.S. corporations and first to hold a sub-Cabinet position in the Treasury Department. He is now a governor of the American Stock Exchange and is on corporate boards, including Prudential Insurance Co. of America, General Electric and the First National Boston Corp.

During World War II, he served three years in North Africa and Italy as the only black in the Army's Criminal Investigations Division in the Mediterranean theater. After the war, he finished college and got his law degree at Cornell. He worked for four years as an assistant district attorney in Frank Hogan's crack Manhattan office and another two years with the U.S. attorney's office in New York. Later, in 1958, he served two years as a judge on New York's old Court of General Sessions, then the city's highest criminal court, but was beaten narrowly by a Democratic candidate in 1960 when he ran for a full 14-year term.

For the last two decades, Pierce has been a partner in the Park Avenue law firm of labor mediator Theodore Kheel, a center of power in New York which commands the respect of labor and the city's leading politicians.

As the head of the litigation section of that firm, Pierce earns "well into six figures" annually, said Kheel, who described Pierce as "slightly sensational."

Pierce appeared to be the least controversial of the Cabinet nominees Reagan announced yesterday and as such was questioned only once as reporters trained on Gen. Alexander M. Haig Jr. about his role in Watergate and James G. Watt about his concern for the environment.

During his one time at the microphone, Pierce did say that he hoped to rehabilitate the South Bronx and other devastated inner-city neighborhoods across the country and would work to "streamline" HUD, which is regarded on Capitol Hill and elsewhere as an extremely cumbersome bureaucracy.

Pierce's appointment brought quiet praise and deep sighs of relief from members of the old civil rights leadership, who had feared that Reagan might name to his Cabinet a black neoconservative eager to sweep away the social programs of the Great Society. Thomas Sowell, a free market economist and senior fellow at Stanford University's conservative Hoover Institution, has been offered the post of secretary of education but turned it down.

Pierce is well-known and admired by members of the civil rights leadership but most of them refrained from saying so publicly.

"I think if any civil rights person says anything good about him, he's in trouble," said one.

"He's a little bit of an elitist," said another person who knows him. "He's got that business of excellence in his head. He's not confused. He knows he's black and he's a competitive guy with [whites]."

Pierce serves as a trustee for a fund-raising arm of the NAACP and has never had any high-profile position in the civil rights movement. But, in a kind of bizarre footnote to his life, Pierce was identified by The Nation magazine two years ago as the man the FBI had hoped in the 1960s would take over leadership of the nation's black movement once the agency had discredited the Rev. Martin Luther King Jr.Pierce said at the time of the disclosure that he knew nothing about the matter and knowledgeable sources corroborated that.