Justice Marshall, who died in 1993, might have topped that joyous outburst last month when John, 41, appointed by President Clinton, was sworn in as the first African-American director of the U.S. Marshals Service, the nation's oldest federal law-enforcement agency. Marshall dropped out of Georgetown in 1980 to become a Virginia state trooper and raise a family (he and wife Jean, 37, have two grown daughters, Melonie and Cecilia); he spent much of the next 14 years working in the field and was known for his tenacity. "He's like a junkyard dog," says an old colleague, senior trooper Dave Powell. In 1994, Marshall was named a U.S. Marshal, nicknamed M Squared, for Marshal Marshall. Director Marshall plans to live up to his father's example. After John's police academy graduation, the justice gave him a pocket-size version of the Constitution and some judicious instructions. "Read this cover-to-cover," he said. "Don't violate it and you'll do fine."