The book, "Increasing Faculty Diversity: The Occupational Choices of High-Achieving Minority Students," reports that roughly 10 percent of high-achieving black and Hispanic college seniors want to become professors -- about the same percentage as whites. But only a small pool of non-Asian minorities earn grades good enough to get them into graduate school. And the study finds that affirmative action is making things worse: It steers minority students to selective colleges where they are underqualified and likely to get lower grades. The low marks make them less likely to attend graduate school. They also erode students' confidence, often convincing them that they aren't suited for academic careers.

The argument that affirmative action disturbs the proper "fit" between most minority students and the colleges they attend has been made for years by conservatives, notably by Thomas Sowell, the economist and columnist currently at the Hoover Institution. The argument says that out of "diversity" concerns, the most selective colleges that usually accept students with 1400 SATs find almost no blacks and Hispanics at that level, so they reach down to take minorities with 1200 scores. The colleges that usually require 1200 scorers then take minorities with 1000 SAT scores, so that on each rung of the campus hierarchy, black and Hispanics are in danger of being overmatched by a fast curriculum and better prepared white and Asian students. The universities get credit for pursuing diversity, but the negative effects of that pursuit don't register with parents or the public.

Studies on the ill effects of preferences are usually shrugged off by academia, but this one may prove unshruggable. It has impeccably liberal sponsors: the Mellon Foundation and the presidents of the eight Ivy League schools. As a result, it is likely to have some impact on the Supreme Court debate over preferences at the University of Michigan. Claude Steele, professor of psychology at Stanford and a member of the study's advisory panel, told the Chronicle of Higher Education that Sandra Day O'Connor's law clerks are likely to notice: "They'll say, 'Look at this. Here's a real thorough study, and it's arguing that affirmative action is harming these kids.'"

The study also undermines two arguments common among "diversity" backers: that discrimination on campus holds down minority achievement and that minorities need mentors and role models from their own racial or ethnic groups. The study says minorities who complained about bias got marks no lower than minorities who reported no discrimination. Faculty encouragement of minorities obviously helps, the study said, but the race or ethnicity of the helpful faculty members made little or no difference.

Stephen Cole, principal author of the book and a sociologist at the State University of New York at Stony Brook, says there is "no quick fix," either for the shortage of minority professors or for the problem of minority students who arrive at selective schools with the deficit of poor educational preparation.

The study concentrated on college seniors in arts and sciences on 34 campuses, including the Ivy League, big-name liberal arts colleges, state universities and historically black colleges. Grade point averages of A or A-minus were achieved by 19 percent of blacks, 27 percent of Hispanics, 40 percent of Asians and 43 percent of whites. Since students with higher grades are most likely to want to become doctors and professors, higher marks for blacks and Hispanics would translate into many more minority professors.

The study is likely to be attacked on this point -- that the way to get more minority professors (and doctors) is to urge black and Hispanic students not to reach for the best colleges, but to be content with mid-range institutions where they are likely to get higher marks. This can easily be portrayed as a back-of-the-bus argument.

But a core finding is that preferential admissions work by creating many disastrous mismatches between students and colleges. Of minorities in the study who got the highest SAT scores (over 1300), only 12 percent attending elite liberal arts colleges had GPAs of A-minus or better. At the state universities (good ones, too) 44 percent of high-scoring minorities had averages of A-minus or better.

Preferential admissions keep drawing many insufficiently prepared blacks and Hispanics onto selective campuses where their chances of succeeding drop dramatically. In what sense is this a progressive idea?