A legal services firm with strong ties to the Democratic Party plans to ask a State Supreme Court justice today to halt a possible runoff election between Fernando Ferrer and Representative Anthony D. Weiner, arguing that it would waste up to $12 million in city funds because Mr. Weiner has already conceded the party's mayoral nomination to Mr. Ferrer.

The firm, the Public Advocacy Group, a private firm that has worked for Senator Hillary Rodham Clinton and Representative Jerrold L. Nadler, among others, is acting on its own to stop a runoff because "it just doesn't make sense to spend taxpayer money when there's no contest," said Chad A. Marlow, a lawyer with the firm. Mr. Marlow was to file the suit today and is a named plaintiff as a New York City Democratic voter.

Mr. Marlow said that the city's Board of Elections had misread state law when it said that a runoff may be required despite Mr. Weiner's concession. According to a copy of Mr. Marlow's suit, which he provided to The New York Times, there are at least eight provisions in the elections statute that allow for halting elections when there are no candidates.

Language in the statute says, for instance, that if an election is uncontested, polling stations do not need to be opened, ballots do not have to be produced, and absentee ballots do not need to be sent to voters.

"There's clearly an out when you don't have a contested election," Mr. Marlow said. "The elections board is correctly reading one part of the law, but in isolation - there are other parts that provide for common-sense flexibility."

The possibility of a costly runoff has alarmed Democratic leaders who fear the unpredictability of such an election. According to the initial ballot count, Mr. Ferrer failed to get 40 percent of the vote in Tuesday's primary, the minimum required to avoid a runoff, but Mr. Weiner, who came in second, conceded the election to him anyway.

Mr. Ferrer was about 250 votes shy of the 40 percent threshold. Frederic M. Umane, the president of the Board of Elections, said yesterday that "by statute, we're locked in" to a runoff if Mr. Ferrer continues to fall short when the official ballot count is certified on Tuesday. "But if someone were to get a legitimate court order," he added, "we would obey it."

Mr. Umane said he had not yet seen a copy of the lawsuit. "They can't argue the law isn't clear," he said. "The law is clear. But what they could say is, 'it's ridiculous.' Based on the equitable powers of the court, there could be a ruling that we should not hold the runoff. And there is a good possibility that we wouldn't object."

Mr. Marlow emphasized that neither Mr. Ferrer's campaign nor any other Democratic Party figures had asked his firm to pursue the lawsuit.

"We're simply progressive Democratic voters who don't want to see money wasted," he said.

The Ferrer campaign has found itself in a political bind over the runoff: It does not want the distraction, or even less the possibility that a Weiner-in-absentia candidacy might do well or even beat Mr. Ferrer. Yet Mr. Ferrer also does not want to be seen as short-circuiting the democratic process or state law, his strategists say.

Should the runoff take place, the city Campaign Finance Board would also be legally obligated to disburse public campaign funds - more than $400,000 for each candidate. Yesterday, however, Mr. Ferrer said he would "absolutely not" accept the money.

Lawyers for Mr. Weiner and Mr. Ferrer met yesterday to discuss approaches that might preclude a potential runoff, but by the end of the day, had not yet settled on a strategy. Neither candidate has yet sought to challenge any of the votes cast. At the Manhattan office of the Board of Elections yesterday, the most frenzied activity was at a table on which sat paper ballots for Council District 8, where Felipe Luciano finished a very close second behind Melissa Mark-Viverito.

Mayor Michael R. Bloomberg himself is - at least publicly - among those who would oppose an uncontested election.

"It's clear who the Democratic candidate is going to be," Mr. Bloomberg said, "but the Campaign Finance Board has to look at their rules and the Board of Elections has to look at their rules. To waste city money that we don't have would be a travesty," he added.

But that is up to the city's Board of Elections, which has the final word on whether Mr. Ferrer has enough votes to avert a runoff.

Yesterday, employees in the board's five borough offices began hand-counting the city's paper ballots, like absentee ballots, the sums for which will later be added to the machine totals collected by board inspectors on Tuesday night and logged into a computer system by police officials.

Today, board employees will open the city's 6,000-plus voting machines - this time at central locations in each borough - and once again verify Tuesday's vote tallies. But under state law, the board may accept paper ballots postmarked by Primary Day through Tuesday, when the board members will certify the results. Because the percentages won by Mr. Weiner and Mr. Ferrer will change as the number of votes tabulated rises, it will not be clear until Tuesday whether a runoff election is required.

"Until we get the final tallies, we won't know how much he has," said Chris Riley, a spokesman for the Board of Elections.