LANSING, Mich. — Local governments and state universities in Michigan can’t offer health insurance to the partners of gay workers, the state Supreme Court ruled yesterday.

The court ruled 5-2 that Michigan’s 2004 ban against gay marriage also blocks domestic-partner policies affecting gay employees at the University of Michigan and other public-sector employers.

The decision affirms a February 2007 appeals court ruling.

Up to 20 public universities, community colleges, school districts, and local governments in Michigan have benefit policies covering at least 375 gay couples. After the appeals court ruled, universities and local governments rewrote their policies to try to comply with the gay marriage ban — so the effect of yesterday’s decision is unclear.

The new policies no longer specifically acknowledge domestic partnerships but make sure “other qualified adults,” including gay partners, are eligible for medical and dental care. The adults have to live together for a certain amount of time, be unmarried, share finances, and be unrelated.

The voter-approved law, which passed 59% to 41%, says the union between a man and woman is the only agreement recognized as a marriage “or similar union for any purpose.”

Justice Stephen Markman, writing for the majority, said that while marriages and domestic partnerships aren’t identical, they are similar.

Dissenting Justices Michael Cavanagh and Marilyn Kelly said the constitutional amendment prohibits nothing more than same-sex marriages or similar unions. They argued that circumstances surrounding the election suggest Michigan voters didn’t intend to take away people’s benefits.

Michigan’s Republican attorney general, Mike Cox, in 2005 interpreted the measure to make unconstitutional existing domestic partner policies at the city of Kalamazoo and elsewhere.