According to a new study by the Civil Rights Project at Harvard University, black and Latino students are now more isolated from their white counterparts than they were three decades ago, before many of the overhauls from the civil rights movement had even begun to take hold.

Nationally, the shift is a result of several factors: big increases in enrollment by black, Latino and Asian students; continuing white flight from the nation's urban centers; and the persistence of housing patterns that isolate racial and ethnic groups. But another big factor, the Harvard study found, has been the termination of dozens of court-ordered desegregation plans.

Spurred by Supreme Court decisions at the start of the 1990's, lower courts have lifted desegregation orders in at least three dozen school districts in the last 10 years. Little Rock, San Diego, Denver and Miami have all come out from under court supervision, and next month a federal judge will reconsider the integration plan in Chicago, the nation's third-largest school district.

A chief principle in the voiding of these orders is one established by the Supreme Court a decade ago: that school districts can be considered successfully desegregated even if student racial imbalances due entirely to demographic factors, like where children live, continue to exist. Largely as a result, black students now typically go to schools where fewer than 31 percent of their classmates are white, the new Harvard study found. That is less contact than in 1970, a year before the Supreme Court authorized the busing that became a primary way of integrating schools.

"We call our schools racially isolated, but it's really just a euphemism for being segregated," said Mary Frances Berry, chairwoman of the United States Commission on Civil Rights. "It has to be regarded as unhealthy. At a time when the society is becoming increasingly diverse, it bodes ill to have increasingly segregated schools."

Many researchers cite sweeping demographic changes, not public policy, as the leading force behind racial separation in the schools. The percentage of students who are members of minority groups has almost doubled in the last 30 years, and, whether as a legacy of enforced segregation, a function of economics or an expression of personal choice, they live largely apart from whites, and often from one another.

Not only did the exodus of white families from cities continue throughout the 1990's, but new suburban enclaves of minorities, particularly African-Americans, also formed, expanding the ring of largely segregated communities beyond the urban core.

But demographics alone cannot account for the rapid segregation of schools, according to the study. As elsewhere, the growth in population among minority students in Southern states has outpaced that of white students for years, and yet the region remained among the nation's most integrated throughout the 1980's, the researchers found. Only in the last decade or so, as courts have declared the schools integrated enough to dissolve desegregation orders, has the segregation between black and white students begun to grow.

"You can't talk about the changes that have happened without talking about the effects of the court orders, particularly in the South," said Erica D. Frankenberg, one of the authors. "The correlation is too strong."

Quite apart from the argument that the school districts are not responsible for correcting neighborhood segregation, some white parents have challenged desegregation plans for considering race at all. Here in Charlotte, white parents filed suit in 1997 contending that their children were being discriminated against because they could not go to schools of their choice. A federal appeals court ruled in their favor in 2001, lifting the district's plan. The Supreme Court declined to hear the case last year, making this fall the first in three decades in which the system did not use race to help determine where children went to school.

The effect was immediate, as schools quickly began to mirror their largely segregated neighborhoods. But while Janice L. Lewis, the principal at Reid Park Elementary here, would welcome the day when she presides over a diverse student body once again, she has few worries that lacking one hurts the caliber of her shiny, almost-new school.

Sprawled out over 18 acres of frost-nipped lawns and untouched trees, Reid Park defies the image of an "inner-city school," as it is often called. Its spacious hallways echo a kind of focused calm that many private schools would envy.

Yet it does have a characteristic common to racially segregated schools: poverty. On average, blacks and Latinos attend schools where roughly 45 percent of the students are poor, compared with 19 percent among whites, a reflection of racial discrepancies in income, the study found. At Reid Park, the number is even higher, with more than 8 in 10 students poor enough to qualify for free or reduced-price lunches.

While few openly question the social importance of integrated schools, as a catalyst for breaking down stereotypes and encouraging tolerance, the debate over academic benefits of integration is a fiery one, often infused with as much ideology as evidence. Some researchers, liberals and conservatives alike, argue that breaking up concentrations of same-race children tends to improve academic performance, especially among black students. Others reject the notion, contending that mixing student populations guarantees little but longer bus rides.

A conviction that predominantly minority schools suffer from scant resources remains one reason why civil rights lawyers are determined to keep desegregation orders in place where they can.

"The bottom line is that all of our experience with desegregation came not from serendipity but through deliberate efforts to change what had been put in place," said Theodore M. Shaw, associate director of the NAACP Legal Defense and Educational Fund Inc. "In that respect, it's also true that if we're going to do anything about racial segregation in the 21st century, it's not going to happen serendipitously."