"Charlie Houston insisted that we be social engineers rather than lawyers," Justice Marshall said in an interview published in the American Bar Association Journal in 1992.

The Justice often credited Mr. Houston, who died in 1950 at the age of 54, as his mentor. Referring to the 1954 Brown v. Board of Education decision, he said in the bar association interview: "The school case was really Charlie's victory. He just never got a chance to see it." A Basic Strategy To End Segregation

After earning his law degree Mr. Marshall opened a law office in Baltimore. The nation was in the fourth year of the Depression. He found himself handling civil rights cases for impoverished clients and was soon $1,000 in debt. But his courtroom victories, including his successful challenge to segregation at the University of Maryland Law School, began to be noticed. In 1936 Mr. Houston, by then the chief counsel of the N.A.A.C.P., recruited him for a $2,600-a-year job on the organization's legal staff in New York. Two years later, when Mr. Houston returned to Washington, Mr. Marshall succeeded to the chief counsel's title but continued to work closely with his mentor.

Pursuing a long-range strategy to eradicate segregation, the two men concentrated first on graduate and professional schools, believing that white judges were most likely to be offended by segregation in that setting and to sympathize with the ambitious young black college graduates who were the plaintiffs in the cases. As successes mounted, the two turned their attention to segregation in public high schools and elementary schools.

"Under Marshall, the N.A.A.C.P.'s legal staff became the model for public interest law firms," Mark Tushnet, one of the Justice's biographers who was also one of his law clerks, wrote in the American Bar Association Journal. "Marshall was thus one of the first public interest lawyers. His commitment to racial justice led him and his staff to develop ways of thinking about constitutional litigation that have been enormously influential far beyond the areas of segregation and discrimination."

In its public school cases, the initial focus of the N.A.A.C.P., and later of the NAACP Legal Defense and Educational Fund, which became a separate entity in the 1940's, was to seek to equalize the resources available to the all-black schools in segregated systems. Mr. Marshall persuaded the organization's board to abandon that approach and to refuse to take on any cases that did not challenge the fact of segregation itself.

The new policy was controversial within the N.A.A.C.P. and prompted resignations by several black lawyers on whom the organization had relied to handle cases in the South. Mr. Marshall was not deterred, and took on many of the cases himself. He traveled constantly and was in charge of as many as 450 cases at a time. "I was on the verge of a nervous breakdown for a long time, but I never quite made the grade," he once said.