OLYMPIA, Wash. — The state Supreme Court upheld Washington's ban on gay marriage Wednesday, saying lawmakers have the power to restrict marriage to unions between a man and woman.

The 5-4 decision leaves Massachusetts as the only state to grant full marriage rights to gay and lesbian couples. It was the latest in a series of significant court rulings favoring gay marriage opponents.

Nineteen gay and lesbian couples seeking to marry had challenged the constitutionality of Washington's 1998 Defense of Marriage Act law, which limits marriage to heterosexual couples. Judges in King and Thurston counties overturned it in 2004, citing the state constitution's "privileges and immunities."

The state appealed, arguing that it has a legitimate interest in regulating relationships that produce children.

Forty-five states have laws banning gay marriage or limiting marriage to between a man and a woman.

In other recent rulings on the issue, courts reinstated voter-approved bans on gay marriage in Nebraska and Georgia, and Tennessee's Supreme Court ruled that voters there should have a say on allowing gay marriage.

Massachusetts' high court -- the same court that issued the historic ruling that has allowed more than 8,000 same-sex couples since 2004 to marry in that state -- ruled a proposed state constitutional amendment to ban gay marriage could go on the ballot if approved by the Legislature.

In Connecticut, a judge found gay and lesbian couples had not been harmed by that state's decision to grant them civil unions but not marriage. Vermont also allows civil unions that confer the same legal rights as heterosexual married couples.

Congress recently rebuffed a move to get a constitutional amendment banning same-sex marriage.