Two Democratic lawyers sued Friday to stop the city from conducting an expensive runoff election in their party's mayoral primary, arguing that the race is uncontested because the second-place finisher agreed to drop out.

Democrats fear a runoff could nip the momentum, exposure and fund-raising that top votegetter Fernando Ferrer (search) would get as the uncontested nominee against incumbent Republican Michael Bloomberg.

Ferrer's three rivals in the primary, including second-place finisher Rep. Anthony Weiner (search) (news, bio, voting record), united behind Ferrer after Tuesday's election. The initial ballot count left Ferrer only about 250 votes short of the 40 percent required to avoid a runoff; but absentee ballots remained to be counted.

The city Board of Elections (search) said Thursday that if Ferrer remains under 40 percent after the final vote count, the law requires a Sept. 27 runoff, which would cost an estimated $12 million. John Ravitz, executive director of the board, said Friday the only way to stop a runoff would be a court order or a change in state law.

Bloomberg said he doesn't want a runoff. "To waste city money that we don't have would be a travesty," he said. Opinion polls show Bloomberg's approval rating steadily climbing and a majority of New Yorkers believing he will win a second term.

The suit by Chad Marlow and Christina Daigneault and their law firm, Public Advocacy Group (search), claimed a runoff would violate the state Constitution and election law.

"The fact that one of the two candidates in the runoff is no longer participating in the election means, under any reasonable interpretation of the word, that the runoff is now `uncontested,'" the suit said.

Daigneault said Friday that the suit was not discussed with party officials or candidates. "We filed this as concerned citizens, as a business that pays taxes and as Democrats who pay taxes," she said.

Marlow told The New York Times that no party figures had asked his firm to sue. "We're simply progressive Democratic voters who don't want to see money wasted," he said.

But Ravitz said, "We are looking at a section of the state election law which clearly states that if no candidate receives 40 percent we have to conduct a runoff."

The firm has worked in the past for Democrats including Sen. Hillary Rodham Clinton and Rep. Jerrold Nadler (news, bio, voting record).