County clerk offices across California opened for their first full day of same-sex marriages Tuesday, with hundreds of happy gay and lesbian couples ready to take the plunge in what in some cities was a party atmosphere.

A gay men's chorus was singing on the front steps of San Francisco City Hall, brighten up by rainbow flags and supporters handing out cupcakes to happy couples.

Helen Zia and Lia Shigemura sang "The Chapel of Love" as they walked to the city attorney's office to get married. The couple, clad in beige jackets and slacks, exchanged vows with Zia's mother by their side.

"This is the most meaningful day of my life. I've always wanted to get married," Shigemura said. "I just never thought it'd be possible."

From San Diego to Eureka, couples readied their formal wear, local licensing clerks expanded their staffs and conservative groups warned of a backlash as the nation's most populous state joined Massachusetts in sanctioning gay unions.

Some couples were from out of state. Unlike Massachusetts, which legalized same-sex marriage in 2004, California has no residency requirement for marriage licenses.

The May 15 California Supreme Court ruling that overturned the state's bans on same-sex marriage became final at 5:01 p.m. Monday, and clerks in at least five counties extended their hours to mark the occasion.

Already, dozens of same-sex couples have seized the opportunity to make their relationships official in the eyes of the law.

In West Hollywood more than 100 people, wearing everything from T-shirts to tuxedoes, were in line when City Hall opened for business at 9 a.m. Six white cabanas with chandeliers and silk flowers were ready for weddings.

Among those getting marriage licenses were actor and gay rights activist George Takei and his longtime partner, Brad Altman; they are planning a September wedding.

"Today we are all here to give flesh and blood reality to that ruling. We are going to make history," said Takei, who played Sulu in the "Star Trek" television series and movies. "Congratulations to all of us and may equality live long and prosper."

Every county was required to start issuing new gender-neutral marriage licenses Tuesday with spaces for "Party A" and "Party B" where "bride" and "groom" used to be.

"Am I Party A or Party B?" Contra Costa County Clerk Stephen Weir jokingly asked his partner of 18 years, John Hemm.

They were the first to marry at Weir's office Tuesday morning. Outside, three opponents of gay marriage from the Westboro Baptist Church picketed, carrying signs with sayings such as "God is your enemy."

Members of the sect are most often seen at military funerals in demonstrations claiming U.S. combat deaths are God's punishment for the nation's tolerance of homosexuality.

The protesters were easily outnumbered by about three dozen supporters of gay marriage, who held signs that read "Hate is not a family value" and "My marriage is not threatened by theirs, why is yours?" Police vehicles lined up near the demonstrators.

On Monday, San Francisco Mayor Gavin Newsom, who helped start the series of lawsuits that led the court to strike down California's one-man-one-woman marriage laws, presided at the wedding of Del Martin, 87, and Phyllis Lyon, 83.

Newsom picked the couple for the only ceremony Monday in City Hall to recognize their 55-year relationship and their status as pioneers of the gay rights movement. More than 650 same-sex couples have made appointments to get marriage licenses in San Francisco before the end of the month.

Newsom called officiating the wedding "this extraordinary and humbling gift." After the mayor pronounced Martin and Lyon "spouses for life," the couple kissed, then emerged to a crowd of well-wishers who showered them with rose petals.

The celebrations are tempered by the reality that in a few months, Californians will go to the ballot box to vote on an initiative that would overturn the high court ruling and again ban gay marriage.

On Monday, three lawmakers and a small group of other same-sex-marriage opponents gathered outside the Capitol to criticize the Supreme Court decision. They urged voters to approve the ballot measure.

"This is an opportunity to take back a little bit of dignity ... for kids, for all of us in California," Republican Assemblyman Doug LaMalfa said. "It really disturbs me that the will of the people was overridden by four members of the Supreme Court."

In both San Francisco and Beverly Hills, where two women became the first same-sex couple in Los Angeles County to marry legally, small groups of protesters waved signs with sayings like "Repent or Perish." They were outnumbered by supporters waving rainbow-striped flags.

Groups that oppose same-sex marriage have pursued several legal avenues to stop the weddings. On Monday, just hours before the ruling went into effect, a conservative legal group asked a Sacramento court to order the California agency that oversees marriages to stop issuing gender-neutral marriage licenses.

A hearing was set for Tuesday.

About two dozen protesters gathered across the street from the Sacramento County clerk's office in the morning, carrying signs that read, "Marriage 1 man + 1 woman" and "Resist Judicial Tyranny."

Juliya Lyubezhanina, 16, came to protest with about 10 other teens from the Slavic Trinity Church.

"They claim to be Christians, but they apparently just don't read the Bible because it's all in there," she said. "It's something to just pray about. It's not a time to be joyful."

A UCLA study issued last week estimated that if the ballot measure is rejected, half of California's more than 100,000 same-sex couples will get married over the next three years, and 68,000 out-of-state couples will travel here to exchange vows.

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Associated Press writers Laura Davis in West Hollywood, Eliott Spagat in San Diego, Juliana Barbassa in San Francisco, Don Thompson in Sacramento, Malia Wollan in Martinez and Jeff Wilson in Los Angeles contributed to this report.