The landmark desegregation ruling and its 30-year legacy.

FROM the nation's Colonial days, Americans have considered education the best vehicle to advance the lot of society. To believe in schooling has been to believe in the future.

It is in school that children learn to get along with others beyond their immediate families. It is in school that young people develop the skills, knowledge, and intellectual discipline they need to prosper. And so, when the civil rights movement for blacks began after World War II, it was inevitable that the battle against racial segregation would eventually be fought in the schools.

The Supreme Court decision in Brown v. Board of Education, the landmark desegregation case in Topeka, Kan., forever changed the face of American schooling. The 30th anniversary of that decision, on May 17, marks a historic milestone.

After the Brown case, ''More than any other institution in American society, the schools became the means through which the goal of equity was pursued,'' says Diane Ravitch, an education historian and author.

A look at the legacy of Brown indicates a divided record. The main success has been the desegregation of black students in the South, due in large part to the much stronger enforcement of civil rights policies in the Southern and border states from 1968 to 1982 than elsewhere. The main failure is the phenomenon of ''white flight,'' primarily in the North, where white families moved from city centers to the suburbs, reestablishing de facto segregation there.

''The whole morality issue of the school desegregation issue disappeared when it moved north,'' Kenneth Clark told an audience recently at Rhode Island College in a gathering to commemorate the Brown v. Board of Education anniversary. Dr. Clark is the black psychologist whose studies on black children's self-perceptions were cited by the Supreme Court in the historymaking litigation filed by the National Association for the Advancement of Colored People.

Because black and Hispanic students far outnumber white pupils in most big cities, Dr. Clark sees a metropolitan or countywide desegregation plan as the only answer for the North.

In 32 of the 35 largest school districts in the United States, minorities make up the largest groups. In these big-city schools 1 student in 10 was minority in 1950. In 1960, 1 in 3 was minority; in 1970 it was 1 in 2; in 1980 it was 7 out of 10. And in 1990, 9 out of 10 students in these districts will be black, Asian, or Hispanic, according to Department of Education data published by the Washington-based Joint Center for Political Studies.

Dr. Clark points to the resolution of an 11-year-old lawsuit in St. Louis as a national model. Nineteen predominantly white Missouri county districts will accept about 15,000 black students from the city's predominantly black schools. White suburban students will be encouraged to transfer to urban magnet schools. Other middle-size cities, like Little Rock, Ark., and Milwaukee, are considering similar plans.

Magnet schools came into vogue in the 1970s in large urban school districts. Their purpose was to promote voluntary integration. They stemmed from the idea that white families would want to enroll their children at inner-city schools offering specialized programs, and minority students would be attracted to similar programs in white areas. Today more than 1,000 magnet schools exist in some 130 of the nation's largest school districts.

But many urban school officials do not see the magnet-school concept as a panacea for desegregation. Instead, they see it and the use of other voluntary measures as ways of creating a handful of elite, though somewhat integrated, schools within a larger, segregated school district.

The creation of many more magnet schools is not feasible because of their costs, says Minneapolis school superintendent Richard R. Green, who presides over one of the few big-city districts in which white students are still in the majority (by a ratio of 60 to 40 percent).

''Our big problem right now is finance. . . . If I get the money, we will begin to show increases in achievement . . . across all racial groups,'' Superintendent Green says. ''So the question of program, the question of alternatives, the question of opportunities - those are no longer questions. We know that we can do them with adequate funding.''

Since coming to office the Reagan administration has made much of magnet schools as a means to foster voluntary desegregation in cities. Federal financing, however, which assisted in creating many magnet schools, has been slashed. Funding fell 94 percent, to $25 million, last year from a high of $400 million in 1979.

At the college level, progress in desegregation has been marked. In 1979 almost 11 percent of the nation's college-age blacks graduated from college, in contrast to only 7 or 8 percent graduating from high school in 1940.

According to the 1980 government survey of seniors, ''Highschool and Beyond, '' 74 percent of Asian-American students planned to attend two- or four-year colleges. Fifty-one percent of whites had plans for college, followed by 44 percent of blacks, 35 percent of Hispanics, and 34 percent of American Indians.

Colleges responded to the post-World War II baby boom by adopting what has been called a ''division of labor between and within institutions.'' Some remained elite in admissions standards and commitment to teaching and research; others were, or became, ''service institutions,'' to prepare students for technical, vocational, or semiprofessional careers.

The concern among higher education officials is that whole campuses or classes of campuses are becoming educational ghettos. This is occurring with Hispanics, who are far more geographically concentrated than the blacks; most Hispanic schoolchildren are in California and Texas. New York, New Mexico, Illinois, Florida, Arizona, and Colorado follow.

In 1980, 54 percent of Hispanic college students were attending two-year institutions - compared with 36 percent of white college students. In California a number of junior colleges are more than 90 percent Chicano.

These figures bring to the college campus the thorny issue of equality of opportunity vs. equality of results. Housing patterns have challenged elementary and secondary schools with this problem in the North. Can the opportunity really be equal, even at the college level, in a racially segregated school?

The great achievement of the Brown ruling was that it struck down the separate-but-equal doctrine. It not only dismantled publicly enforced dual school systems but necessarily led to the elimination of state-enforced racial segregation. Yet for the rest of this century, elementary and secondary schools in many cities will, in fact, remain segregated.

Urban educators, like their suburban counterparts, are caught in a wave of reform proposals calling for educational excellence. Given urban demographics, this is an appropriate interim objective for schools. The Brown ruling never precluded excellence, just separateness. The national agenda still calls for the elimination of segregated schools.