Writing on behalf of the high court in one of Monday’s landmark civil rights cases, Justice Sandra Day O’Connor offered a passionate defense of the value of diversity in our institutions of higher learning.

She approvingly referenced the late Justice Lewis Powell, who observed 25 years ago that “nothing less than the nation’s future depends upon leaders trained through wide exposure to the ideas and mores of students as diverse as this nation of many peoples.”

Nothing less than the nation’s future. That is why, O’Connor concluded, the court endorses “Justice Powell’s view that student body diversity is a compelling state interest that can justify the use of race in university admissions.”

But at the same time she penned such a clear, reasonable defense of the University of Michigan Law School’s affirmative-action program, O’Connor joined with a majority of her colleagues and struck down the university’s undergraduate admissions program. Why? Because minority applicants were given a numerical advantage in that school’s 150-point rating system.

Those minority kids weren’t the only ones chalking up the extra points, it must be noted. Michigan residents got 10; children of alumni, 4; athletes, the same 20 points as a black or Latina.

But the very automatic nature of the racial bonus persuaded O’Connor and her less liberal colleagues that a number, any number, was unfair.

So the nation is now left with a challenging dilemma: How do we get from here to there?

If numerical systems are disallowed, how can giant public institutions like Michigan, which receive tens of thousands of applicants a year, ensure the student body diversity so prized by the court, so essential for the nation’s future?

If race is only one of those amorphous “factors” that somehow may be considered in the admissions process but not too loudly and surely not with any number attached how then do we create opportunity for the next generation of minority doctors, lawyers, teachers, accountants?

There seems to be only one answer. If the playing field for college and graduate school admission is to be “leveled” for whites, then the playing field in elementary and secondary education must be leveled for disadvantaged minorities.

If the conservative justices on the Supreme Court are so offended by the use of race in higher education, then they should be equally offended by the way race affects the allocation of resources, talent and attention in public education.

They should be offended that black and Latino students are more segregated in impoverished school districts than at any time in the past three decades, according to the Harvard Civil Rights Project.

They should be outraged that black, Latino and low-income students are far less likely to have highly qualified teachers and be enrolled in challenging curriculums than white students, according to the Education Trust. And that the only children guaranteed quality preschool education in Pennsylvania are the ones whose parents can afford it.

They should be concerned about the persistent gap in achievement that leaves even suburban, affluent black students lagging behind their white schoolmates.

They should be outraged, too, that a culture of learning and achievement is often absent from many impoverished communities, consigning those children who do want to work hard and succeed with scant support from their families, neighbors and schools.

Addressing this issue isn’t a job just for the Supreme Court, of course. We all should be offended, concerned, outraged.

The rationale for affirmative action has evolved from a broad redress of historic wrongs to a more limited mechanism for ensuring diversity. So be it. Now the challenge is to meet that goal. Nothing less than the nation’s future depends on it.