Clarence M. Pendleton, chairman of the United States Civil Rights Commission, died yesterday after collapsing while exercising at a San Diego hotel health club. He was 57 years old and lived in San Diego and Washington, D.C.
Mr. Pendleton died of an apparent heart attack at 11:13 A.M. at the Mission Bay Hospital after efforts failed to revive him, according to David Lodge, the San Diego Deputy Coroner.
He was riding a stationary bicycle at the time of his collapse at the Hilton Beach and Tennis Resort, the officials said.
Mr. Pendleton came to the attention of Ronald Reagan in 1980 when he switched to the Republican Party, abandoning his self-described ''bleeding-heart liberalism.'' Guided by Edwin Meese 3d, the confidant of Mr. Reagan, Mr. Pendleton went to work in support of Mr. Reagan's bid for the Presidency. A year later, Mr. Reagan, as President, appointed him as the first black chairman of the Civil Rights Commission.
As its chairman, Mr. Pendleton was an outspoken proponent of the Administration's ''color-blind'' philosophy on civil rights.
From the time of his appointment on Nov. 16, 1981, Mr. Pendleton was at the center of a political storm. He took several stands that most observers would not have expected from a black on the rights commission.
Mr. Pendleton, for example, opposed desegregation through busing because he believed that such action violated the principle of neighborhood schools. He also doubted that predominantly white schools were necessarily better than predominantly black ones.
In addition, he denounced affirmative action as a ''bankrupt policy'' that detracted from the legitimate achievements of those who would have succeeded in any case. 
Mr. Pendleton would respond quickly and sharply to his critics, many of whom were from the black community, offering to match his record against ''anyone else's rhetoric any day.''
He said he believed that the commission, under his chairmanship, was criticized because the civil rights community arrogated the moral high ground and scorned anyone, especially anyone within the conservative Reagan Administration, who did not ''embrace every tenet of the liberal orthodoxy on civil rights.''
''I think there are people who would like to see the commission go out of business,'' he concluded after Congress cut the agency's budget in 1986 by $4.1 million, giving it $7.5 million that year as against $11.6 million the previous year.
He believed that Congress cut the budget to force him to resign. ''But despite public perception, we aren't missing a beat,'' he said.
Nevertheless, many of the commission's top staff members left, either out of frustration or because their jobs were eliminated as a result of budget cuts. And activity slowed at the agency. 
''Penny'' as Mr. Pendleton was known, was described last night by several friends, including high officials of the Administration, as candid, iconoclastic and sensitive.
''He was a man of total and complete candor,'' said William Bradford Reynolds, the Assistant Attorney General for Civil Rights and a close friend of Mr. Pendleton. ''He was a man who felt very deeply that the individuals in America should deal with one another as brothers and sisters totally without regard to race and background.''
Although Mr. Pendleton was sometimes regarded by civil rights groups as antagonistic to their causes, his friends said he cared deeply about individual rights.
''He probably was the messenger bearing a message that many did not want to hear,'' Mr. Reynolds said.
Colleagues on the commission expressed shock and sorrow at the reports of Mr. Pendleton's death.
''Penny was a unique individual, and we will miss him a lot,'' said Robert A. Destro, who served on the commission with Mr. Pendleton. ''It doesn't make much difference whether someone was a supporter or disagreed with him, we thought he was wonderful human being.''
Mr. Destro said that at the time of Mr. Pendleton's death, he and the chairman were ''taking a hard look at'' the civil rights of American Indians and the medically dependent. 
Mr. Pendleton, born on Nov. 10, 1930, in Louisville, Ky., grew up in Washington, D.C., where his father was the first swimming coach at Howard University and an assistant director of the District of Columbia's recreation department.
He graduated from Dunbar High School, where many children of black middle-class families were educated. He then followed in the steps of his grandfather, a lawyer in Baltimore, and his father by enrolling in Howard.
He earned a Bachelor of Science degree in 1954 and worked briefly for the District of Columbia recreation department before joining the Army. On released from the Army in 1957, he returned to Howard, where he had excelled as a swimmer, and took a post as a physical education instructor.
In 1970, Mr. Pendleton became a director of the urban affairs department of the National Recreation and Parks Association. Two years later, he moved to San Diego to serve as director of the Model Cities program there.
In 1975, he became head of the San Diego Urban League and was the only one out of more than 150 officers in the League to support Ronald Reagan's bid for the Presidency.
He is survived by is wife, Margrit, their daughter, Paula, and a son and a daughter by a previous marriage, George and Susan.