LOS ANGELES -- Urie Bronfenbrenner, a cofounder of the federal Head Start program and a professor whose theories profoundly altered the understanding of what children need to develop into successful adults, died Sunday after a long illness at his home in Ithaca, N.Y. He was 88.
An emeritus professor of psychology at Cornell University, Dr. Bronfenbrenner argued that individuals develop not in isolation but within a system of relationships to family and society. He called his theory the ecology of human development.
He believed that keeping the family intact -- particularly ensuring that children have regular, sustained interaction with their parents, not just sporadic ''quality time" -- was one of the most critical challenges facing society. For several decades he provided a strong voice for programs and policies to counter the forces impinging on the family, the breakdown of which he said was readily apparent in worrisome rates of teenage pregnancy, drug abuse, violence, and other problems.
His advocacy of parent involvement in their children's education led to his appointment in 1965 to a federal panel that laid the foundation for Head Start, the school readiness program that has served 20 million disadvantaged children and families in the past 40 years.
According to Melvin L. Kohn, a Johns Hopkins University sociologist and former student of the Cornell professor, Dr. Bronfenbrenner's work impelled social and behavioral scientists to ''realize that interpersonal relationships, even [at] the smallest level of the . . . parent-child relationship, did not exist in a social vacuum but were embedded in the larger social structures of community, society, economics, and politics."
Born in Moscow, Dr. Bronfenbrenner moved with his family to the United States when he was 6.
He studied psychology and music at Cornell, where he earned a bachelor's degree. He received a master's in education from Harvard University and a doctorate in developmental psychology from the University of Michigan in 1942.
The day after he received his PhD, he entered the Army and served as a psychologist during World War II. He joined the Cornell faculty in 1948.
In 1964, he testified at a congressional hearing, urging that President Johnson's War on Poverty be broadened to target poverty's most vulnerable victims, children. His remarks earned him an invitation to the White House for tea with Lady Bird Johnson, who wanted to discuss child-care programs he had studied.
He became one of three developmental psychologists on the planning committee whose work led to the development of Head Start. The other two psychologists were Mamie Clark and Edward Zigler, a Yale child development expert who is often referred to as the ''father" of Head Start.
Their work laid the foundation for the landmark program, which features parental involvement as a cornerstone.
In later years, Dr. Bronfenbrenner was sharply critical of rising materialism, which he said was encouraging parents to spend more hours away from home working in order to afford nice things for their children. He saw it as just one of several societal forces that were reducing crucial family time and exacerbating the alienation of American youths.
He urged families to regularly make time to interact and learn from each other in activities as low-key as taking a walk together. Dr. Bronfenbrenner emphasized that the activity was less important than ''what's in between" -- a conversation or other interaction with a caring adult. Such interactions, he said, were a boost to a child's healthy psychological development and an essential strategy for combating the deterioration of the family.
He wrote 14 books, including ''Two Worlds of Childhood" (1970), a comparison of American and Soviet childrearing.
The father of six children, he acknowledged that juggling the demands of work and parenthood had often challenged him.
At the conclusion of a 1970 White House conference on American children at which he spoke, the Cornell scholar was asked by an assistant to President Nixon to extend his stay by one day. Dr. Bronfenbrenner, however, wanted to return home for a family birthday celebration.
''I said, 'I can't,' " Dr. Bronfenbrenner recalled in an interview many years later. The presidential aide ''said in a stern voice, 'Are you putting your own children ahead of the children of this country?' I said, 'yes.' "
According to The New York Times, Dr. Bronfenbrenner leaves his wife of 63 years, Liese; two sons, Michael, of Seal Beach, Calif., and Steven, of San Anselmo, Calif.; four daughters, Beth Soll of New York City; Mary and Kate, of Ithaca; and Ann Stambler of Newton, Mass.; 13 grandchildren, and one great-grandchild.