The university said Ms. Fisher would not have been admitted even if race had played no role in the process, and it questioned whether she has suffered the sort of injury that gives her standing to sue. But the university’s larger defense is that it must be free to assemble a varied student body as part of its academic and societal mission. The Supreme Court endorsed that view by a 5-to-4 vote in 2003 in Grutter v. Bollinger.

University officials said that the school’s affirmative action program was needed to build a student body diverse enough to include minority students with a broad range of backgrounds and for the campus to have a “critical mass” of minority students in most classrooms. Interaction among students in class and around campus, said Kedra Ishop, the university’s director of admissions, helps students overcome biases and make contributions to a diverse society. “The role of U.T. Austin,” Dr. Ishop said, “is to provide leadership to the state.”

The majority opinion in the Grutter case, written by Justice Sandra Day O’Connor, rejected the use of racial quotas in admissions decisions but said that race could be used as one factor among many, as part of a “holistic review.” Justice O’Connor retired in 2006, and her replacement by Justice Samuel A. Alito Jr. may open the way for a ruling cutting back on such race-conscious admissions policies, or eliminating them.

Admissions officers at colleges and universities almost universally endorse the idea that students from diverse backgrounds learn from each other, overcome stereotypes, and in so doing prepare themselves for leadership positions in society. Many critics of affirmative action say that there is at best a weak correlation between race and having a range of views presented in the classroom.

Others say the Constitution does not permit the government to sort people by race, no matter how worthy its goal. “While racial diversity on college campuses is beneficial, it cannot be attained by racial discrimination,” said Edward Blum, an adviser to Ms. Fisher and a driving force behind the Fisher case.