LOS ANGELES — In a unanimous decision, the California Supreme Court ruled Monday that illegal immigrants can be eligible for the same reduced tuition at public colleges and universities as legal residents of the state.

The ruling is the latest in a series of high-profile battles about state immigration policies. In addition to Arizona’s strict new immigration law, which the United States Department of Justice has challenged in court, nine other states have laws similar to California’s, with lawsuits pending in Nebraska and Texas.

Currently, students who attend at least three years of high school in California and graduate are eligible for in-state tuition at public schools, which can save them as much as $12,000 a year compared with students who come from other states.

Illegal immigrants remain ineligible for state or federal financial aid.

The California court ruled that the 2001 state law does not conflict with a federal prohibition on education benefits for illegal immigrants based on residency, in part because United States citizens from other states who attend high school in California may also benefit.

“It cannot be the case that states may never give a benefit to unlawful aliens without giving the same benefit to all American citizens,” wrote Justice Ming W. Chin, one of the court’s more conservative justices, in the court’s opinion.

Kris Kobach, the legal scholar who helped draft Arizona’s immigration law, argued the case on behalf of American citizens from other states who were not eligible for reduced tuition — his latest effort to enact tough illegal immigration policies in states across the country. He said his side would appeal the ruling to the United States Supreme Court.

“I think the pendulum is definitely swinging in favor of enforcement of the law and discouraging illegal immigration,” Mr. Kobach said. “I am confident this is not the last word on the subject.”

In California, Latinos now make up more than half of all students in public schools, according to the State Department of Education, and strong support from Latinos helped Democrats here fare better than they did in most other states in this year’s midterm elections.

Supporters of immigration overhaul hope that legislation that would offer some illegal immigrant students access to federal financial aid and a path toward citizenship will be taken up again in the lame-duck session of Congress that convened Monday.

“This law makes higher education affordable for so many students who have the added difficulty of not being eligible for federal financial aid,” said Thomas A. Saenz, president and general counsel for the Mexican American Legal Defense and Educational Fund. “If they are both ineligible for aid and then face higher tuition rates, it becomes virtually impossible for students to go on to higher education.”

Kevin R. Johnson, dean of the law school at the University of California, Davis, said that the ruling might discourage future lawsuits in other states with similar laws, but that litigation about students who are illegal immigrants would continue.

“This issue is not going to go away,” Professor Johnson said. “It’s going to require some Congressional action.”