Roy Wilkins, 80, a Mississippi slave's grandson who helped shape many of the most important moments in U.S. civil rights history as executive director of the National Association for the Advancement of Colored People, died of uremia yesterday at New York University Medical Center in New York City.

He was hospitalized Aug. 18 for treatment of heart and kidney ailments.

Mr. Wilkins guided the NAACP, the nation's largest and oldest civil rights group, through its time of greatest growth and prestige. He also presided over what many regard as the beginning of the NAACP's political and financial decline.

From 1931, when he joined the organization's staff as assistant secretary, until 1977, when he retired as executive director after 22 years in that post, Mr. Wilkins and the NAACP were one. He and the association were at the forefront of the drive for antilynching laws in the 1930s, when lynching was a familiar occurrence in backward reaches of the South and Midwest.

He was the administrator of the NAACP in 1954 when it won the historic Brown vs. Board of Education decision in the U.S. Supreme Court. The ruling overturned the court's 1896 decision in Plessy vs. Ferguson which, under its "separate but equal" doctrine, had provided the legal justification for racial segregation in the United States.

Mr. Wilkins was a key supporter and organizer of the March on Washington on Aug. 28, 1963. That dynamic lobbying effort brought nearly 250,000 people to the nation's capital. Largely influenced by the march, the assassination of President John F. Kennedy on Nov. 22, 1963, and consultation with Mr. Wilkins throughout those events, President Lyndon B. Johnson pushed for and won approval of the landmark 1964 Civil Rights Act. This made support for voting rights, equal employment and equal access to public accommodations a matter of federal law.

Many who remember the 1963 event place another famous civil rights leader, the Rev. Dr. Martin Luther King Jr., at its center. A gifted orator, Dr. King "stole the show," as many blacks said, with his "I Have a Dream" speech. Five years later, on April 4, 1968, Dr. King was assassinated on a balcony of the Lorraine Motel in Memphis, Tenn.

But the role of Mr. Wilkins in organizing the demonstration was enormous. To the chagrin of friends such as Joseph L. Rauh, a Washington lawyer who has been active in behalf of civil rights and civil liberties all his professional life, the public and the media often made comparisons between Dr. King and Mr. Wilkins, contrasting their styles and commenting on their effectiveness.

"I hated that. But you were always driven to make those comparisons," Rauh said. "I guess you can say Martin was the front man who changed public opinion. But Roy was the one who was able to use that shift in public opinion to bring about legislation and legal rulings that benefited blacks, as well as any number of other people."

Mr. Wilkins and Dr. King "complemented one another, but not in an intentional way," Rauh said, adding, as others have, that there was some style-based "antipathy between the two men."

"Roy wasn't the . . . one out front. He was the one in the back who got things done," Rauh said.

On the death of Mr. Wilkins, President Reagan and other leaders hailed not only what he did in his life, but the way he did it and what he stood for.

The president said that Mr. Wilkins "worked for equality, spoke for freedom and marched for justice. His quiet and unassuming manner masked his tremendous passion for civil and human rights."

Vice President Bush said that the dedication of Mr. Wilkins "to the poor, to those bypassed by our society and to those threatened by discrimination and hate were based on a deep and burning conviction that all Americans must be guaranteed equality and opportunity."

Benjamin Hooks, the current NAACP executive director, said Mr. Wilkins was "a towering figure in American history. His name will stand on top of the list of those who loved their country and did their best to make it better."

Carl Holman, the president of the National Urban Coalition, said that "Roy was the last of a very special breed of black leader who saw himself as a kind of quiet militant very much concerned about -- and devoted to -- his people. And he was just as much a convinced patriot who believed his country could never be all that it was meant to be as long as it denied some of its people their rights."

Mayor Marion Barry of Washington said, "Roy Wilkins was a personal inspiration to me and countless other young people in the civil rights movement" who "left behind a legacy of achievement, of cooperation and of progress."

The Rev. Jesse Jackson, the head of Operation PUSH, said Mr. Wilkins "bore more than his share of his responsibility for the nation's advancement."

The Wilkins way of getting things done usually was a slow, studied process, often involving expensive legal fights. Progress and setbacks frequently walked hand-in-hand, a frustrating fact to those who did not share his dedication to working within the system.

Frustration led to anger among many blacks; and anger led to the urban riots that set the 1960s ablaze on American soil.

In those turbulent days, Mr. Wilkins would remind his usually young and militant critics that he and his organization were working for civil rights long before they joined the cause. But NAACP membership rolls continued to decline, from a high of more than 500,000 in the 1960s to about 400,000 today.

Ironically, both Mr. Wilkins and his organization were victims of their own success. In many cities, black and white children go to school together today as if they had always been allowed to do so. Though a disproportionate number of blacks are in the nation's lower economic strata, a new generation of middle class blacks, largely beneficiaries of the battles fought by Mr. Wilkins, enjoys education, job and housing privileges once withheld from many of their parents.

In Marshall, Tex., for example, a black father recently told this reporter that once he "couldn't believe" that his children would ever be allowed to attend the formerly all-white, now integrated, Marshall High School.

"But, damn, my girl is going to be teaching there this year," the man said. "Can you believe that? We used to walk way around that school when I was here," said the man, who taught at the formerly all-black Pemberton High School (now an integrated intermediate school) in Marshall, but who now works for the federal government in Los Angeles. "Things really have changed."

The man's daughter is in her early 20s. She knows about Mr. Wilkins and his fight for civil rights because her parents taught her about the man and his work. But many of her black peers in Marshall say they never heard of Roy Wilkins, or have little knowledge of who he was.

"That's not only the case in places like Marshall. There are blacks in many cities who know little or nothing of Roy Wilkins and the NAACP," said Nathaniel Jones, who was the chief counsel of the NAACP for 10 years and now is a judge on the 6th U.S. Circuit Court of Appeals in Cincinnati.

"Roy used to say that the NAACP is in business to go out of business," the judge said. "Many of the people who don't know anything about him are where they are today because of his work."

Mr. Wilkins was a complicated man, according to those who knew him. Behind the doors of his New York City office, "he might explode" over a staff flub, one friend and associate said. "But he would never explode in public combat. He was a very smooth, uncompromising strategist in that arena," the friend said.

The Wilkins manner was evident during the racial discord that erupted in Boston in 1974 and 1975 as a result of a school desegregation program requiring busing. The incumbent administration of President Gerald Ford, eyeing the upcoming 1976 election, critics say, indicated that it might side with antibusing forces led by the Boston School Committee. Vocally militant civil rights leaders such as the Rev. Jackson strongly attacked the Ford administration's approach to the Boston busing problem.

But Mr. Wilkins worked behind the scenes, urging his civil rights, business and labor allies to talk to Ford and then attorney general Edward H. Levi. The administration, which was leaning toward supporting the committee's request to delay implementation of the busing order, backed off.

Style can carry a lobbyist a long way in the corridors of Washington power, as Mr. Wilkins discovered in his relationship with the late President Johnson.

Never were two men more different. Mr. Wilkins was the urbane scholar and editor -- he had worked as managing editor of the black Kansas City Call and had edited The Crisis, the NAACP magazine, from 1934 to 1949 -- who had spent most of his young adult life in an integrated neighborhood in St. Paul, Minn. Johnson was the archetypical Texan, a political gut-fighter up from South Central Texas who twisted legislative arms with all the grace of a cowboy branding cattle.

With the civil rights cauldron coming to full boil in the mid-1960s, President Johnson needed an influential black he could trust as much as Mr. Wilkins needed the power of the presidency to push civil rights programs through Congress. Mr. Johnson was attracted to Mr. Wilkins' penchant for thoroughly researching issues and options, his understanding of the uses of power, and his lack of an appetite for the limelight.

Roger Wilkins, an assistant attorney general in the Johnson administration, a journalist and a nephew of Roy Wilkins, recalled that his uncle and Mr. Johnson "were always talking to one another, checking with each other."

The younger Wilkins said that he met Mr. Johnson at a reception in New York City six months before the former president died of a heart attack on Jan. 22, 1973.

"He asked me what I was doing, and I told him," Roger Wilkins said. "Then, I asked him what he was doing. He said he had left the presidency and was looking for work. So I told him that, as a private citizen, he should speak up for civil rights.

"He said, 'That sounds like a good idea, but who can I talk to about it?' I told him he should speak to someone he knows and trusts, my uncle. He said, 'Of course, you're right about that.' "

A month before he died, after having talked with Roy Wilkins, Mr. Johnson addressed a civil rights conference at the Lyndon Baines Johnson Library in Austin, Tex., and "gave one of the best, goddamndest civil rights speeches you ever heard," Roger Wilkins said.

Roy Wilkins was born Aug. 30, 1901, in St. Louis. His parents were William D. Wilkins and Mayfield Edmondson Wilkins. His mother died of tuberculosis when he was 3. His father, alone and unable to care for Mr. Wilkins and his younger brother and sister, sent the three children to live with an aunt and uncle in St. Paul.

The neighborhood in St. Paul where Mr. Wilkins lived was poor, but ethnically diverse, affording him an early opportunity to experience other cultures. He attended the city's nonsegregated schools, edited his high school newspaper and, in 1919, enrolled in the University of Minnesota, where he studied journalism and sociology.

Then as now, and even at a public institution, college was expensive for the poor. Mr. Wilkins paid for his education by cleaning out stockyards and working as a dining car waiter and redcap, while holding down a position as night editor of the school newspaper, the Minnesota Daily.

After receiving his bachelor's degree in 1923, Mr. Wilkins joined the staff of the Kansas City (Missouri) Call, one of a number of newspapers then exclusively dedicated to the interests of black Americans. He quickly became managing editor of the newspaper. But more than that, he developed a sense of moral outrage, largely because of the strict racial segregation that existed in Kansas City.

"He came from a place which was relatively free of racial prejudice, for the times," said Lucille Bluford, a longtime friend of Mr. Wilkins who worked with him on The Call. "Black people couldn't go to certain places, live in certain places or do certain things in Kansas City then, and that really got on Roy's nerves."

In addition to his writing, Mr. Wilkins began to work for the Kansas City branch of the NAACP. His efforts attracted the attention of NAACP national secretary Walter White, then the association's top official. White brought Mr. Wilkins to New York to work for the national organization.

To continue his education about what it was like to be a black in the Deep South in those days, Mr. Wilkins would disguise himself as a laborer and travel through the region. On one of these trips, he and a black companion tried to get work on a federally funded construction project in Mississippi.

Both got hired and both experienced poor treatment on the job. The fact that Mr. Wilkins had no callouses on his hands aroused suspicion among white foremen that he was no ordinary field hand. Mr. Wilkins said he had been working lately as an elevator operator. His reports to the NAACP about his experiences led to a Congressional inquiry into racial discrimination on federal projects.

"Roy really loved his job," said Henry Lee Moon, who spent most of his adult life working as Mr. Wilkins' press secretary. "He was reluctant to leave office, and some people criticized him for trying to hold on to the position too long. But he was kind of that way.

"This was his life's work," Moon said. "He was dedicated to it. It really meant a lot to him."

Mr. Wilkins is survived by his wife of 51 years, the former Aminda (Minnie) Badeau of Jamaica, Queens, N.Y.