Stephan Thernstrom offers nary a caveat as he lays out what he sees as some unvarnished truth about the performance of African Americans in higher education. Blacks are far more likely than other students to drop out of college, to not complete law school and to fail the bar exam, he says.

His conclusion: "Preference programs" often thrust African American students in over their heads, setting them up for failure. Many in the luncheon audience at the Independent Women's Forum nod in agreement. But his wife and co-lecturer, Abigail Thernstrom, winces through much of his talk. "He's all facts and figures," she complains later. "Sometimes, he can be like fingernails going across a blackboard."

Not that she disagrees with his conclusion. In fact, she offers a few strong -- and controversial -- points of her own to the audience.

As the Thernstroms see it, so long as people are identified by race and treated differently because of it, the country's long, dark history of racism will be perpetuated. Failure to fully appreciate the nation's progress is as dangerous as racism itself, they say. Moreover, racial preferences, as they describe many affirmative action programs, often hurt blacks.

They detail those arguments in a new book hailed by some conservative activists as the most important treatise about race in years.

"America in Black and White: One Nation Indivisible" is an optimistic tome -- suspiciously so, say its critics. It uses a broad array of polls, surveys and government statistics to sketch a sunny portrait of black progress and improving racial attitudes in America.

The authors say the reality that black-white relations, once unspeakably bad, have improved immensely is often overlooked, but has profound implications for America's ongoing conversation on race. "It seems extraordinarily hard for liberals to say we have come a long way from the days of the Jim Crow South and the appallingly racist North," Abigail Thernstrom says. "It is hard for conservatives to say, Yes, there has been a terrible history of racism in this country, and indeed that racism has not disappeared.' "

That simple message has catapulted the Thernstroms to the front lines of a war in which they have long been loyal soldiers: the crusade for a "colorblind" society, free of race-conscious government programs like affirmative action.

The movement has gained much ground in recent years, including a slew of court victories and voter approval last fall of a ban on government affirmative action programs in California. Even with that, colorblind advocates have never quite shaken opponents' damning charge that they are motivated by racism. The Thernstroms' new book, they believe, offers fresh evidence for vindication.

"I really believe it is the biggest book on race in a long time," says Clint Bolick, litigation director of the Institute for Justice, a conservative public interest law firm. "I think that it is testimony to the deep substance of the book. They are out to prove their case, not simply throw rhetoric."

That the Thernstroms, self-described 1950s liberals, now stand on the cutting edge of conservatism as Americans wage one of the nation's most contentious public policy debates is an irony they sometimes find humorous. But it is also a circumstance they cite as evidence of liberalism's failures.

"We haven't changed," Stephan Thernstrom says. "It is that liberalism has evolved." His wife quickly adds, "I feel sad that the classic civil rights message is now called conservatism." Liberal Upbringing

Abigail Mann and Stephan Thernstrom met while they were both graduate students at Harvard, during a 1958 lecture by I.F. Stone, the leftist journalist. They married several months later.

Stephan, 62, is a working-class son of Port Huron, Mich., who won a debating scholarship to Northwestern University and then attended Harvard.

Abigail, 61, is a New Yorker who attended the Little Red School House, a Greenwich Village private school staffed by communists and suspected communists who were banned from teaching elsewhere. She later went on to Barnard College and Harvard.

"My parents traveled in communist circles," she says. "The hard-left society was racially integrated. I think that was important to me."

Through the peak years of the civil rights movement, the couple shared what they call "standard liberal views." They were among the white activists who picketed Woolworth's to protest segregation of the chain's Southern lunch counters. And they were preparing to travel to Mississippi to register black voters in 1964, a plan that was derailed when Abigail became pregnant with the first of the couple's two children.

Through the years, Stephan became a highly regarded historian, authoring several books and editing The Harvard Encyclopedia of American Ethnic Groups. But he became the object of protest in 1988, after his classroom lecture touching on problems in the black family was criticized by some black students as racially insensitive. Students complained to administrators and the matter was chronicled in the Harvard Crimson, drawing broad attention to a conflict that he insists had no merit. He was left bitter after receiving "less than a ringing endorsement" from Harvard administrators, who took no action against him. The incident has since been cited by conservative activists as an example of political correctness run amok.

Abigail, meanwhile, made her mark in the 1980s as an early and widely quoted critic of many affirmative action efforts, particularly voting districts drawn with the sole intention of having majority black or Hispanic populations. Her book, "Whose Votes Count?: Affirmative Action and Minority Voting Rights," is cited as one of the first to challenge minority voting districts.

She is now a senior fellow at the Manhattan Institute, a conservative think tank, and sits on the boards of several other conservative groups, including the Institute for Justice and the Center for Equal Opportunity.

"I'd say we've stuck to our principles over the years: Don't judge people on the basis of the color of their skin," Abigail says.

While their adamant opposition to affirmative action helped convince several conservative foundations to fund their book research, the two say they are hardly right-wing ideologues. For example, in a cutting book review, Stephan denounced Dinesh D'Souza's "The End of Racism," and its "generalizations about civilization differences' between blacks and whites."

Rather than seeking to push a broad conservative agenda, the Thernstroms say the real intention of their book is to reframe the debate about race relations in America, a topic they believe is often driven by less-than-illuminating anecdotes and overheated rhetoric.

Black men have a hard time catching a cab? Just who are these cabdrivers anyway? the Thernstroms may ask. Are they white? If not, does that prove pervasive white racism, or something else? Do the attacks on affirmative action and other black gains make the end of the 1990s similar to the 1890s, as some civil rights leaders assert? Please, the Thernstroms say, don't do that kind of disservice to the huge amount of racial progress made since the end of the 19th century, when racist violence was literally family entertainment in much of America.

It is a point of view that invites broad debate. "The central problem of blacks in higher education is not access to college, but graduating from college," Stephan Thernstrom says during the couple's recent talk before the Independent Women's Forum in downtown Washington. "Affirmative action is not cost free."

When black attorney Faye Anderson, who says she was able to attend Stanford Law School only because of affirmative action, protests that numbers don't tell the whole story and that the cultural atmosphere on a campus might have something to do with black achievement, Stephan seems curious. But the facts are the facts, he concludes. "Students should go to the law schools where their college {grade point averages} or {law school board} scores indicate they'll be average," he says.

Abigail Thernstrom seems more willing to explore the gray areas of racial interaction. She allows that maybe things can be changed in the "culture and context" of law school to make black students feel more at home. But her bottom line is the same. "I want diversity, too," she says in her soft, raspy voice. "But I don't want to get it this way." History With a Purpose?

While their cool but candid tone and the sweep of their research is winning wide praise in conservative circles, some on the left say the couple is doing little more than providing intellectual cover for damaging conservative policies.

"In effect what they are saying to black Americans is, Hey, what are you complaining about? Look at all the things we have done for you. We are letting some of you in the middle class. . . . What is all the whining about?' " says Andrew Hacker, a Queens College political scientist whose 1992 book, "Two Nations: Black and White, Separate, Hostile, Unequal," painted a portrait of an America plagued by white supremacy.

The Thernstroms call their book an answer to Hacker and others who paint a dismal picture of American race relations. But beyond providing their own view of the nation's black-white racial dynamics, the Thernstroms offer some partisan and controversial conclusions.

They say the irreversible march of black progress in America began during World War II and climaxed in the 1960s civil rights revolution but has been slowed by three major forces: the increased popularity of black nationalism, the use of race-conscious remedies such as affirmative action and the sharp increase in violent crime among African Americans.

"Nothing has been more harmful to the black community, and nothing has done more to poison race relations, than the explosion of black violent crime since the 1960s," the authors write.

Harvard law professor and presidential adviser Christopher Edley Jr., in an article published in Harvard, the university's alumni magazine, challenges their assessment. "The Thernstroms' history-with-a-purpose seems designed to make a comic-book-simple point: Things used to be really bad, and civil rights liberals have led us astray by failing to recognize the important progress that has been made," he says. "The real argument lies elsewhere. The disagreement about civil rights today concerns not the historical record but the needed pace of progress now."

On that point, the Thernstroms are willing to give ground. They say their book is hardly the last word on race. Instead, they see it as an attempt to shed some light on a subject shrouded in misinformation. "This is simply an effort to draw a series of maps, to supply data, to teach how to weigh evidence," Abigail says. "Other people are going to be critics of our analysis. That's great. The data are there for them to analyze." CAPTION: Stephan and Abigail Thernstrom argue that America has made progress in race relations. Their critics say their data fuel attacks on affirmative action. CAPTION: Abigail and Stephan Thernstrom's "America in Black and White: One Nation Indivisible" contends that improvements in black-white relations are overlooked.