Clarence M. Mitchell Jr., 73, a lifelong champion of equality for blacks who played a key role in winning passage of much of the major civil rights legislation of the 1960s, died last night at the Maryland General Hospital in Baltimore.

As the chief Washington lobbyist for the NAACP for nearly three decades, Mr. Mitchell combined conviction, persistence and quiet persuasive power. In his ultimately successful quest for the landmark measures of the '60s, he displayed skills and talents that won him the sobriquet of "the 101st Senator."

Both as the NAACP's man in Washington, and as a principal in the Leadership Conference on Civil Rights, which he helped found, Mr. Mitchell was instrumental in passage of the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968.

A lawyer and a former newspaper reporter whose career was galvanized when in 1933 he witnessed his first lynching, Mr. Mitchell was a leading member of a family that in Maryland, his home state, and in Baltimore, his hometown, symbolized civil rights and the NAACP.

Known as a man of courage and integrity, Mr. Mitchell persisted optimistically through years of resistance and rebuff to seek the common ground and consensus that in time permitted him to witness passage of the bills that helped guarantee equality before the law.

Despite his successes, his name was not nearly so well known to the general public as many of the other principal actors in the social and legislative revolution of the 1960s.

Firmly committed to the goal of full integration of blacks into the American mainstream, Mr. Mitchell shunned the separatist doctrine and militant tactics that might have won him greater visibility.

A modest and unassuming man, whose arena of action was the congressional office and conference room, he neither sought nor attained the broad public recognition to which his accomplishments entitled him.

Before the days in which meaningful civil rights legislation was possible, Mr. Mitchell prompted and promoted advances through executive orders, such as the one by which President Truman demanded the desegregation of the armed forces.

During the Eisenhower administration, Mr. Mitchell was credited with guiding to passage the 1957 Civil Rights Act, the first legislation of its kind in years. He was also recognized among legislative insiders as being instrumental in passage of the 1961 act that set up the federal Civil Rights Commission.

Beyond his work in shepherding to passage the civil rights bills of the '60s, Mr. Mitchell is cited as the author of a key section of at least one of them, Title VII of the 1964 bill, which required equal employment opportunity.

As chairman of the leadership conference on civil rights, Mr. Mitchell employed his lobbying skills in helping to bring about the rejection by the Senate of the nominations to the Supreme Court of Clement Haynsworth and G. Harrold Carswell.

Despite the not infrequent bitterness and strong feelings bound up in the long struggle in which Mr. Mitchell was engaged, he was himself viewed as generous and conciliatory towards his foes, often finding it possible to say a good word about all but the harshest among them.

A man who carried a picket sign to help desegregate Baltimore schools, and who was arrested for going through the main door of a South Carolina railroad station, Mr. Mitchell knew the values of direct action.

But, he said, "you've got to know when to stop picketing and sit down at the conference table."

In 1980 the year he left his leadership conference post, and two years after leaving the NAACP post, Mr. Mitchell received the nation's highest civilian honor, the Presidential Medal of Freedom, from President Carter.

He was also appointed as a U.S. representative to the United Nations by President Ford, and at the time of his death, was a member of the board of regents of the University of Maryland, from which he held his law degree.

Mr. Mitchell was born in Baltimore, where he lived for the last four decades at the same inner-city address. His father, a musician, and his mother, a cashier, enforced daily study hours for their seven children, who included Mr. Mitchell's brother, U.S. Rep. Parren J. Mitchell (D-Md.).

"He was one of the most remarkable human beings I've ever met," Rep. Mitchell said last night of his brother.

Sen. Paul Sarbanes (D-Md.) called Mr. Mitchell "a great champiion of justice and human dignity" who was "a powerful force for a better America."

John Toll, president of the University of Maryland, described his death as a "serious loss" for the nation and called him "an inspiring leader" in the work for equality, justice and a better society.

After receiving a bachelor's degree from Lincoln University in Chester, Pa., Mr. Mitchell became a reporter for the Baltimore Afro-American newspaper. The lynching he saw as a newsman in Princess Anne, Md. made him decide on a civil rights career.

After work for the Urban League in the Midwest, he joined the federal government in assignments that included enforcing World War II antidiscrimination orders in shipyards. He was labor secretary of the NAACP from 1945 until becoming director of the Washington bureau in 1950.

In recent years, he and his wife Juanita, the first black woman to practice law in Maryland, were joined by a son, Michael, a Baltimore City Councilman, in the firm of Mitchell, Mitchell and Mitchell. Another son, Clarence III, is in the state legislature.

Survivors include two other sons, Keiffer J., and George D.