John R. Searles Jr., 93, an urban planner who led the effort to clear the slums of Southwest Washington in the 1950s and to put modern architecture, highways and parks in their place, died Oct. 21 at a retirement home in Ponte Vedra Beach, Fla., where he had lived since 1979. He had prostate cancer.

Mr. Searles was executive director of the powerful Redevelopment Land Agency, a branch of the District government, from 1951 to 1961. Under his guidance, the agency embarked on a dramatic effort to redevelop Southwest Washington and Foggy Bottom.

Throughout the 1950s, the agency bought properties and cleared entire neighborhoods of what Mr. Searles and other civic leaders considered unsafe, dilapidated housing. The monumental exercise in urban renewal -- which The Washington Post called "the most ambitious project of its type in the nation" -- was seen, depending on one's perspective, as either visionary or callous.

Inspired by the resurgent downtowns he had seen emerging from European cities damaged in World War II, Mr. Searles sought to bring a similar spirit of modernism to Washington. At first, his ideas were seen as a sensible way to rid the city of what The Post described as "a sore spot of crime, illegitimacy, refuse and disordered lives." But the Southwest project had unforeseen consequences that disrupted an entire community.

From 1954 to 1960, the old rowhouses and alleyways of Southwest were demolished, along with hundreds of small businesses. About 20,000 residents, most of them African American, were forced to find new homes. Black leaders derided the plan as "Negro removal."

Two property owners challenged the authority of the redevelopment agency and the federal government in a case that reached the Supreme Court, but the court ruled in 1954 that the urban renewal plans were constitutional.

Writing in The Post, Mr. Searles extolled the parks of Copenhagen and the vibrant urban dynamism of Rotterdam, but that rosy vision of Southwest Washington never developed. Instead, it remained largely desolate until highways, large office buildings and apartment houses were built in the 1960s and 1970s.

Former residents were resettled in public housing in Northeast Washington and elsewhere. But even with better construction and utilities, many of them painfully felt that the fabric of their community had been torn from under them.

In the book "City of Magnificent Intentions: A History of the District of Columbia" (1997), a shopkeeper who had been in business in Southwest for more than 50 years summed up his experience: "Well, it seems like they're handin' out a passel o' joy and a passel o' sorrow."

John Rumney Searles Jr. was born in Detroit on Oct. 14, 1912, and was a graduate of Princeton University. In 1940, he received a master's degree from Wayne State University in Detroit. Then he served in the Army for five years.

He came to Washington in 1946 to work with the Housing and Home Finance Agency, a forerunner of the Department of Housing and Urban Development. In 1951, he took over the Redevelopment Land Agency, which had been created by Congress in 1949.

Described by The Post as "outgoing, eloquent, persuasive and perceptive," Mr. Searles built the agency into a model of its kind, with a staff of 90 and a mandate to change the city's urban core. He rejected an early plan by landscape architect Elbert Peets to reshape Southwest by blending new buildings with older structures.

Instead, Mr. Searles recommended a plan to level much of the area and start anew, a method then seen as a progressive solution to urban blight. The Post called it "the most heartening change in the face of Washington for a generation."

Mr. Searles stepped down from the agency in 1961, the same year Jane Jacobs's influential book "The Death and Life of Great American Cities" was published. Her central point was that cities thrived best when their close-knit, traditional neighborhoods were preserved, with minimal intrusion from highways and large-scale building projects.

From 1962 to 1978, Mr. Searles was chief executive of the Metropolitan Development Association of Syracuse, N.Y., where he led planning efforts for the city and region and helped launch the Syracuse Symphony Orchestra. From 1975 to 1979, he was chairman of Onondaga County's Fair Employment Practices Board, which promoted affirmative action programs in Upstate New York.

He received the Rockefeller Public Service Award in 1956 and awards from the D.C. government for meritorious service. He also consulted on urban development programs in Detroit, Baghdad and Athens. He retired to Florida in 1979.

Survivors include his wife of 62 years, Leota Dell Johnson Searles of Ponte Vedra Beach; three children, Elisabeth Friedberg of New York City, John R. Searles III of Jacksonville, Fla., and James C. Searles of Santa Cruz, Calif.; and five grandchildren.

Under John Searles Jr., about 20,000 people, most African American, and hundreds of small businesses were displaced.