SAN FRANCISCO — POLICE chief Frank Jordan stunned incumbent Art Agnos Tuesday, garnering more than 30 percent of the popular vote to force a Dec. 10 mayoral runoff election.Mr. Jordan's strategy to concentrate on signing up absentee voters paid off early as he grabbed what proved to be an insurmountable lead when the polls closed. "We have proven we can win," said Jordan. "And we are confident the result will be even more stunning in five weeks time." Mayor Agnos, who was voted into office in 1988 with the largest majority in a local mayoral election this century, was never able to recover from the early onslaught. However, he did see signs for hope since he was able to close to within 6,348 votes with 56 percent of the precincts reporting. "This campaign has been a crisis for me in my political life, but you people [his supporters] have stood with me and given me strength," he said. "Now I have the strength to wage a winning campaign over the next five weeks." Still, the loss understated the disintegration of Agnos's patchwork of neighborhood coalitions and a growing discontent among residents with the city's handling of its rapidly growing homeless problem. "I've been called tough and abrasive," Agnos said. "But how is Frank Jordan going to stand up to those who have challenged this city? His answer so far when asked about the problems within the police department when he ran it is that I was the mayor. Well, if he couldn't stand up with me how will he stand up against those who will challenge our diverse lifestyle here in San Francisco." Supervisor Angela Alioto, who had gone to court earlier on Tuesday in an attempt to keep the polls open two extra hours, finished a distant third. A ballot proposition to repeal the city's year-old domestic partners law was also soundly defeated. Developments prior to the election had thrown a shiver of fear through the supporters of the city's year-old domestic partners law. The law, which gives many of the same bereavement and hospital visitation rights to registered unmarried couples, both gay and straight, as those enjoyed by their married counterparts, faced a repeal measure on Tuesday. Despite a last-minute campaign launched by Archbishop John Quinn, the repeal measure was soundly defeated. "Looking at the results tonight tells us that this has become an issue that no longer is limited to just one community within the city," said Amy Neches, of the "no" on Proposition K campaign. "Domestic partners has gained broad-based support."