Polls indicated a virtual dead heat between Green, the city's public advocate, and Ferrer, the Bronx borough president. The winner advances to the November election to take on billionaire media magnate Michael Bloomberg in the race to replace popular Mayor Rudolph Giuliani.
Green, voting in Manhattan early Thursday morning, said, "Third time's the charm. ... The final question for the verdict of voters is who's the strong independent Democrat to lead the New York comeback, to bring us together, keep jobs here and educate our kids."
Ferrer, after voting in the Bronx, said, "New York City faces some daunting challenges. As mayor, I'll rebuild our city and revitalize our economy, but I won't abandon our commitment to improving education, expanding after-school programs, strengthening police-community relations, and making health care and affordable housing more accessible."
Manhattan resident Matthew Segall, 77, said he picked Ferrer as a protest vote.
"I'm voting against Green," Segall said. "As public advocate, he's done nothing."
Robin Aufses, a 51-year-old English department administrator at a Long Island school, said she voted for Green. But she said she wasn't sure he was equipped to handle the nation's biggest city in the midst of its greatest crisis.
"I hope so," she said, "but what one person could?"
Giuliani, a two-term Republican, has been lauded for his leadership in the aftermath of the attacks on the World Trade Center. He flirted briefly with the idea of trying to challenge term-limit laws and remaining in office for a third term, but backed off and said he could stay on to help in the transition.
Many observers believe Ferrer has a slight advantage over Green because polls show his base of Latinos, blacks and members of the health and municipal labor unions are more loyal and better energized than Green supporters.
Green, the front-runner for much of the summer, has spent the last several days trying to maintain his support in the black community while attempting to energize the white vote, where he hopes to capture more than four of every five votes.
"A dead heat in the polls means you go look at the guy who can turn out his voters, so (Ferrer's) got a very good shot," said Baruch College political science professor Douglas Muzzio. "Green's strategy has to be to hold on to his black vote while going after moderate and liberal whites. For him, white voters have to turn out in big numbers."
Ferrer, who is trying to become the city's first Hispanic mayor, spent much of Wednesday with union members in Manhattan, appearing with hospital workers, teachers and municipal workers at a get-out-the-vote rallies.
"So it's all come down to this. One more day," a beamin Ferrer told the hospital workers. "It's been a lot of hard work."
Green campaigned in areas with large numbers of moderate white voters, saying he believes momentum is on his side after a late charge by Ferrer in recent months.
"The tide is turning," Green said.
The race turned hostile earlier this week after a television campaign ad by Green questioned Ferrer's leadership skills. The ad called Ferrer "borderline irresponsible" and suggests he would "divide our city."
In response, the Ferrer campaign put together a hastily assembled television ad of its own which accused Green of breaking his promise not to engage in negative campaigning.
Green has also criticized Ferrer's spending proposals, which include giving teachers a significant pay raise and providing money for after-school programs.
Ferrer defended the moves as necessary improvements even as the city faces new priorities.
The victor will have survived a campaign unique in city history, one that was nterrupted when two hijacked jetliners crashed into the trade center; one in which the candidates were eclipsed by a lame-duck incumbent.
The attacks occurred on day of the scheduled primary, which was pushed back two weeks.
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