Phyllis Lyon and Del Martin fell in love at a time when lesbians risked being arrested, fired from their jobs and sent to electroshock treatment.

On Monday afternoon, more than a half-century after they became a couple, Lyon and Martin plan to become the first same-sex couples to legally exchange marriage vows in San Francisco and among the first in the state.

"It was something you wanted to know, 'Is it really going to happen?' And now it's happened, and maybe it can continue to happen," Lyon said.

San Francisco Mayor Gavin Newsom plans to officiate at the private ceremony in his City Hall office before 50 invited guests. He picked Martin, 87, and Lyon, 84, for the front of the line in recognition of their long relationship and their status as pioneers of the gay rights movement.

Along with six other women, they founded a San Francisco social club for lesbians in 1955 called the Daughters of Bilitis. Under their leadership, it evolved into the nation's first lesbian advocacy organization. They have the FBI files to prove it.

Their ceremony Monday will, in fact, be a marriage do-over.

In February 2004, San Francisco's new mayor decided to challenge California's marriage laws by issuing marriage licenses to same-sex couples. His advisers and gay rights activists knew right away which couple would put the most compelling human face on the issue: Martin and Lyon.

Back then, the couple planned to celebrate their 51st anniversary as live-in lovers on Valentine's Day. Because of their work with the Daughters, they also were icons in the gay community.

"Four years ago, when they agreed to be married, it was in equal parts to support the mayor and to support the idea that lesbians and gay people formed committed relationships and should have those relationships respected," says Kate Kendell, a close friend and executive director of the National Center for Lesbian Rights.

Lyon and Martin vividly recall the excitement of being secretly swept into the clerk's office, saying "I do" in front of a tiny group of city staff members and friends, and then being rushed out of the building. There were no corsages, no bottles of champagne. Afterward they went to lunch, just the two of them, at a restaurant run as a job training program for participants in a substance abuse program.

"Of course, nobody down there knew, so we were left to be by ourselves like we wanted to be," said Martin, the less gregarious of the two. "Then we came home."

"And watched TV," added Lyon.

The privacy was short-lived. Their wedding portrait, showing the couple cradling each other in pastel-colored pantsuits with their foreheads tenderly touching, drew worldwide attention.

Same-sex marriage would become legal in Massachusetts in another three months, but San Francisco's calculated act of civil disobedience drove the debate.

In the month that followed, more than 4,000 other couples followed Martin and Lyon down the aisle before a judge acting on petitions brought by gay marriage opponents halted the city's spree.

The state Supreme Court ultimately voided the unions, but the women were among the two dozen couples who served as plaintiffs in the lawsuits that led the same court last month to overturn California's ban on gay marriage.

They were having their morning coffee when Lyon heard the news on the radio. She rushed across the house to embrace Martin. Not long after, Newsom called to offer congratulations and to ask if they would be willing to be at the forefront yet again.

"Sure," was the answer they gave.

The couple, who live in the same San Francisco house they bought in 1956, do not get out much now. Martin needs a wheelchair to get around. Although they plan to briefly greet well-wishers at City Hall after the ceremony, they are having a private reception for friends and family.

"It's so endearing because they do seem excited and a little bit nervous," Kendell said. "It's like the classic feelings anyone has as their wedding day approaches."

Because a few other clerk's offices agreed to stay open until the court's decision becomes final at 5 p.m. PDT, other couples planning late afternoon weddings may already have tied the knot before the mayor pronounces Lyon and Martin "spouses for life."

They don't mind. They know they already are.

"We get along well," Lyon said. "And we love each other."

"I love you, too," Martin said.