PHOENIX - A federal judge on Thursday blocked state officials from interceding in a court case involving how best to ensure that the Tucson Unified School District is properly desegregated.

U.S. District Judge David Bury rejected arguments by Attorney General Tom Horne that he needs to be sure that plans being formulated for the district do not include the kind of "ethnic studies" courses that are prohibited by a 2010 state law. The judge said such a request is premature, given the plans for the district have yet to be formulated.

But Bury also said the state law may be legally irrelevant. The judge said he will not allow Horne or that controversial statute to stand in the way of finally resolving the 38-year-old desegregation lawsuit involving TUSD.

"This case is first, foremost, and only about desegregation in the TUSD," Bury wrote. That case is built around federal laws prohibiting racial discrimination.

"Any state law or state interest found to be contrary to or an impediment to the desegregation mandated … must yield to the supremacy of the federal Constitution," the judge said.

There are two separate legal issues that have now become entwined.

The first stems from a 1974 lawsuit charging the school district with discrimination, a case that resulted in federal court oversight of policies and practices.

TUSD sought to end that oversight with promises of complying with a settlement agreement. But a federal appellate court said Bury can cancel that oversight only if the district demonstrates over time that it will comply.

Bury then appointed Willis Hawley as a special master to work toward that goal.

What caused the latest dust-up is that special master said he intends to create "culturally relevant curricula" for Mexican-American students - curricula that could be considered by some to violate that 2010 law.

That law makes it illegal for any school to have courses that promote the overthrow of the United States government, promote resentment toward a race or class or people, or advocate ethnic solidarity instead of the treatment of students as individuals. The law also precludes courses "designed primarily for pupils of a particular ethnic group."

TUSD canceled its Mexican American Studies program after state school Superintendent John Huppenthal ruled that its courses run afoul of the law and threatened to withhold 10 percent of state aid to the district as the statute requires.

Horne told Bury he wants to be part of the desegregation lawsuit to ensure anything the special master proposes does not reinstate either those programs or institute anything else that falls within what the state law precludes.

Aside from declaring the supremacy of federal anti-discrimination laws, Bury said Horne is off-base.

"The state's argument for intervention presumes any ethnic studies included in the (special master's plan) will necessarily violate (the law)," the judge said.

Bury said if Horne has any concerns, he remains free to meet with the special master, both before the initial plan is presented to the court on July 5 or after that date.

But Horne said late Thursday that simply being able to consult - or even to file a "friend of the court" brief as the judge agreed to let him do - is insufficient to protect the state's interests in not having programs he believes are discriminatory.

Horne also said it is wrong to assume that some type of ethnic studies is necessary to end discrimination in TUSD. In fact, he said, the reverse is true.

"The point of ethnic studies is to divide people," he said.