Washington ? President Bush, stepping into the most politically charged affirmative action case in a generation, asserted Wednesday that a program of racial preferences for minority applicants at the University of Michigan was “divisive, unfair and impossible to square with the Constitution.”

Democrats and civil rights leaders swiftly attacked Bush’s position in a Supreme Court case that could overturn a 1978 affirmative action ruling and jeopardize 25 years of race-based programs.

“The Bush administration continues a disturbing pattern of using the rhetoric of diversity as a substitute for real progress on a civil right agenda,” said Sen. John Kerry, D-Mass., a candidate for the Democratic presidential nomination.

Sensitive to such criticism, the White House said a brief being filed today on Bush’s behalf is narrowly tailored to oppose the Michigan program and does not address a critical question: whether race can play a role at all in selecting a student body. Bush chose to let the Supreme Court settle an issue that could reshape affirmative action programs nationwide.

The court hears the case in March.

Some conservatives, including senior members of Bush’s own Justice Department, had urged Bush to take a tougher stand against ever using race. In an unusual foray into domestic policy, national security adviser Condoleezza Rice participated in the discussions and eventually sided with Bush’s split-the-difference approach.

Rice, who is black, opposed quotas as provost of Stanford University.

The Michigan program “amounts to a quota system that unfairly rewards or penalizes prospective students solely on their race,” Bush said.

He said the undergraduate admissions program awarded black, Hispanic and native American students 20 points, one-fifth of the total normally needed for admission. “Quota systems that use race to include or exclude people from higher education and the opportunities it offers are divisive, unfair and impossible to square with the Constitution,” Bush said.

The last Supreme Court case that addressed affirmative action in college admissions banned the outright use of racial quotas but still allowed universities to use race as a factor. The case, the 1978 Bakke ruling, involved a white applicant rejected from a public medical school in California.