SAN FRANCISCO - In a monumental victory for the gay rights movement, the California Supreme Court overturned a voter-approved ban on gay marriage Thursday in a ruling that would allow same-sex couples in the nation's biggest state to tie the knot.

Domestic partnerships are not a good enough substitute for marriage, the justices ruled 4-3 in an opinion written by Chief Justice Ron George.

Outside the courthouse, gay marriage supporters cried and cheered as news spread of the decision.

"Our state now recognizes that an individual's capacity to establish a loving and long-term committed relationship with another person and responsibly to care for and raise children does not depend upon the individual's sexual orientation," the court wrote.

The city of San Francisco, two dozen gay and lesbian couples and gay rights groups sued in March 2004 after the court halted San Francisco's monthlong same-sex wedding march.

"Today the California Supreme Court took a giant leap to ensure that everybody — not just in the state of California, but throughout the country — will have equal treatment under the law," said City Attorney Dennis Herrera, who argued the case for San Francisco.