A late surge by Rep. Anthony Weiner may have forced a September 27 runoff with Fernando Ferrer for the Democratic mayoral nomination, but with thousands of ballots outstanding, the race remained too close to call early today.

Shortly after 9 p.m. last night, it appeared that the front-runner throughout the 2005 Democratic mayoral campaign, Mr. Ferrer, had captured the 40% of the vote needed to win the nomination. As the minutes ticked by and more precincts reported, however, his margin of victory dwindled, and the percentage of the electorate he captured fell, and fell. With 100% of precincts reporting, Mr. Ferrer had 39.95% of the vote and Mr. Weiner had 28.82%.

Only about 17.5% of the city’s 2.6 million enrolled Democrats turned out for the primary.

The other two well-known Democrats in the race, C. Virginia Fields and Gifford Miller, were far behind. Ms. Fields, Manhattan borough president, had about 16%, and Mr. Miller, the City Council speaker, had 10%. Two minor candidates split about 5% of the vote.

Though all the precincts had reported, absentee ballots and paper ballots have yet to be counted. The Board of Elections sent out 25,399 absentee ballots, of which 8,422 valid ones had been returned. More than 13,000 could still be received and counted, according to elections officials, who expected to start tabulating those results tomorrow. Officials said they wouldn’t know how many paper ballots are outstanding until they open the boxes tomorrow.

“Under the law those ballots we receive a week after the election we have to count,” the executive director of the Board of Elections, John Ravitz, speaking on NY1, said of the absentee ballots.

The question of whether either campaign might challenge yesterday’s count and demand a recount remained unanswered.

“I love this city,” Mr. Weiner said. “I will not divide it.” He said he would rather lose the nomination “than do anything that leaves this city in tatters.”

The Weiner campaign said, however, that every vote counts and the race for the nomination was far from over. The congressman’s campaign spokesman, Anson Kaye, said: “The number is 39.9. … If the numbers hold there, the rule is 40 and under, and that’s where we are.”

Mr. Ferrer’s campaign spokeswoman, Jennifer Bluestein, said the campaign hopes not to have to go to court to resolve who won yesterday’s vote.

“We have to count the paper, which won’t be started until we open up the back of the machines, and then we’ll see if Freddy Ferrer has the votes he needs to avoid a runoff,” a spokesman for the Board of Elections, Christopher Riley, said.

Earlier in the evening, before it was clear what the results would be, the mood was tense at the four Manhattan restaurants and ballrooms where the Democrats and their supporters gathered to await the results, as supporters and pollsters shared their pet theories about how the low turnout would impact their candidates.

The only place that was jubilant all night was the ballroom of the Brooklyn Marriott, where crowds of high-profile supporters and volunteers gathered to cheer on the Republican incumbent, Mayor Bloomberg, who did not face a primary challenge.

Food and drinks were sparse at the Democratic gatherings. There were cash bars, with a ginger ale at the Miller gathering costing $6 and a Jack Daniels at the Fields “victory party” costing $9. The only food available at Ferrer event was crudites, while there was no food at all at the Fields party.

Meanwhile, Mr. Bloomberg, a self-made multi-billionaire who is financing his own campaign, served popcorn, pigs in blankets, and chips, and offered his backers an open bar.

Before the final results were clear last night, about 10 p.m., Mr. Bloomberg took the stage and, surrounded by sign waving, cheering supporters, he talked about his vision for the city and his record of accomplishments in reducing crime, improving schools, and creating housing and jobs.

In the months to come before the November election, he said, “professional politicians” would be attacking his record.

“I’m not a professional politician, something I’m proud of,” he said, looking happier than he’s looked throughout the campaign, even as he received some of the city’s most prized endorsements.

“If we continue to fight crime, reform our schools and create new jobs, I’ll tell you who the real winner will be on November 8, the people of New York. Am I right?” he said to loud applause.

Meanwhile, back across the Brooklyn Bridge, the Democrats were watching the poll results live on large screens at their respective events.

Early on at the Weiner event, his supporters said they thought the congressman, who represents sections of Queens and Brooklyn, could win the requisite 40% outright and avoid a runoff. Mr. Weiner started the race off in the single digits but began to shoot up in the polls in recent weeks.

Mr. Weiner’s father, Morton, said he has faith in his son.

“He’s always been a tough fighter in sports, arguing, and debate,” he told The New York Sun. “I’m very proud of everything Anthony’s accomplished so far. I always think Anthony will come out on top.”

Mr. Weiner was the last of the candidates to appear at his own event. He took the stage just before midnight, and, to chants of “Weiner, Weiner,” talked about some of his goals as mayor – and what he plans to do in the coming weeks.

Mr. Weiner said he respects his Democratic rival, and looks forward to competing with him in a “vigorous” campaign.

“I like Freddy Ferrer,” he said. “I’m going to like him once we unify this party as well. To the extent that we have differences they will based on policy, not on personality.”

At the Ferrer event, supporters including H. Carl McCall, State Attorney General Eliot Spitzer, and a number of members of the state Assembly and the City Council watched NY1’s continuous coverage on two screens as Mr. Ferrer watched the results at an undisclosed location with his family.

After 11 p.m., Mr. Spitzer proclaimed yesterday a “wonderful victory for New York” as he introduced Mr. Ferrer. Mr. Spitzer, who is expected to run for governor next year, said, “We want a real Democrat to be mayor of the city of New York.”

Chants and cheers for Mr. Ferrer didn’t last for the 20 seconds it took for him to make it to the stage. When he arrived, he delivered what sounded like a victory speech without declaring victory.

“The road has been long, my friends, but this journey has been worth it,” he said. “And we’re almost there, because we’re about to make history, and in eight weeks we’re going to change history.”

Mr. Ferrer’s supporters said last night that a runoff election might not be a bad thing.

“It doesn’t matter,” the state Assembly speaker, Sheldon Silver, said.

Mr. McCall, the former state comptroller, said: “A runoff would give Fernando Ferrer an opportunity for people to see him.”

He noted that so far interest in the race has been limited, telling The New York Sun that yesterday, he “ran into people who weren’t aware it was Election Day.”

At the Miller event, which was held at a Chelsea club, the mood was sad. Joined by supporters from the council, including Eric Gioia and David Yassky, the Upper East Side council speaker gave an early concession speech.

“We had a campaign based on ideas and a vision for the city’s future,” he said. “I love this city and I pledge to work tirelessly to help the nominee beat Bloomberg.”

Ms. Fields – who, like Mr. Miller, was forced by term limits to give up her current job – conceded soon after, saying she was “proud” of her campaign.

Mr. Bloomberg’s supporters said the low turnout was a victory for the mayor.

“Democratic voters found the cast of Democratic mayoral candidate so uninspiring that they chose to save their vote for November when they could vote for Mike Bloomberg’s reelection,” a Bloomberg adviser and faculty member at New York University, Mitchell Moss, said.