SAN FRANCISCO, March 14 - In a victory for city officials here, a state judge ruled on Monday that California's ban on same-sex marriage was unconstitutional, overturning a statewide proposition passed in 2000 that defined marriage as between a man and woman.
In a tentative ruling, the judge, Richard A. Kramer of San Francisco County Superior Court, said "the denial of marriage to same-sex couples appears impermissibly arbitrary," thus violating the equal protection clause of the state's Constitution. The ruling will not be made final until the judge meets with the various parties to the litigation on March 30.
While welcoming the decision, which came in a lawsuit filed by the city against the state, Mayor Gavin Newsom of San Francisco said it was "only the beginning" of a long legal battle that would probably be decided by the California Supreme Court. Mr. Newsom said marriage licenses would not be offered to same-sex couples in San Francisco while the litigation was pending.
"We will continue to respect the decisions of the court," Mr. Newsom said.
Even so, celebrations erupted at City Hall, as same-sex couples crowded into a news conference held by Mr. Newsom and other city officials, and gay and lesbian leaders said there would be revelry throughout the evening in the Castro, the city's best-known gay district. Marches and rallies were announced in at least a dozen other cities across the state.
Superior Court Judge Richard A. Kramer struck down two California laws that limited marriage in the state to a union of opposite-sex couples. The ruling came one year after San Francisco made worldwide headlines when it opened its city hall to same-sex weddings over Valentine's Day weekend through March 11 2004.

Kramer said the two California laws violated the state's constitutional guarantees of privacy and a legal concept called due process - which tries to ensure each person is treated equally by the law. "The denial of marriage to same-sex couples appears impermissibly arbitrary," Kramer wrote in the opinion released Monday.

In his decision, Kramer cited United States Supreme Court case law ranging from ''Brown v. Board of Education'' to ''Lawrence v. Texas'' in a step-by-step dismantling of legal arguments against same-sex marriage. Including the following excerpts:
*'''Traditional definition of marriage:''' "Same-sex marriage cannot be prohibited solely because California has always done so before."
*'''With California's domestic partner laws, gays don't need marriage:''' "That California has granted marriage-like rights to same-sex couples points to the conclusion that there is no rational state interest in denying them the rites of marriage as well."
*'''The purpose of marriage is procreation:''' "The obvious natural and social reality is that one does not have to be married to procreate, nor does one have to procreate in order to be married." 

Kramer, a Catholic Republican Judge appointed by Pete Wilson, California's previous conservative governor, issued a "stay" on his order, making it a tentative decision by delaying its implementation for 60 days to allow the same-sex marriage opponents time to file an appeal to his ruling. The case is widely expected to be brought before the California Supreme Court.

Less than a year ago, the state's Supreme Court annulled more than 4,000 same-sex marriages which took place in San Francisco County in 2004. The court did not rule on the constitutionality of same-sex marriages, but ruled more narrowly that San Francisco mayor Gavin Newsom overstepped his authority by unilaterally deciding not to follow state laws he did not agree with instead of challenging the laws in court, which is the proper legal way to overturn or affirm laws in California and much of the United States.