Mayor Bloomberg’s current and erstwhile Republican opponents have teamed up in an effort to force a GOP primary. The former mayoral candidate, Steven Shaw – who said Sunday that he was dropping out of the race – will attempt to transfer more than 2,000 ballot-access petition signatures to Mr. Bloomberg’s remaining Republican rival, Thomas Ognibene, the two challengers said yesterday.

“My signatures weren’t doing any good sitting around,” Mr. Shaw told The New York Sun. “And I think it’s important that there is a primary, and I’m doing everything I can to make sure there is one.”

Earlier this week, the chances of a Republican primary, which would be held September 13, seemed slim. Democratic or Republican candidates for citywide office need 7,500 signatures from voters registered in their parties to be granted primary-ballot access, and as of Sunday Mr. Ognibene had only 6,000.

Yesterday, hours before the petition-filing deadline, the former City Council minority leader from Queens said he had between 7,700 and 7,800 signatures. Mr. Shaw, an investment banker who lives in Brooklyn, said he had signed a form declining his petitions and requesting that the signatures be made over to Mr. Ognibene instead, a move that would bring Mr. Ognibene’s total close to 10,000. Last month, at the beginning of the petitioning process, Mr. Ognibene said he sought 15,000 signatures to secure a foolproof buffer against challenges to his petitions by Bloomberg-campaign election lawyers.

A spokesman for the Bloomberg campaign, Stuart Loeser, declined to comment on whether the mayor – who filed approximately 24,000 petition signatures with the Board of Elections on Monday – would challenge Mr. Ognibene’s signatures.

If Mr. Bloomberg mounts a successful challenge to Mr. Ognibene’s petitions and thus avoids a Republican primary, Mr. Ognibene, who is a lawyer, has pledged to take the matter to federal court.

“The way the law is set up with 7,500, the only people who are going to make it is multibillionaires,” Mr. Ognibene said. “It’s a ballot-access question – from the 1965 Voting Rights Act. It’s a constitutional issue.”

Yet while a last-minute Shaw-to-Ognibene switch could help avoid what Mr. Ognibene perceives to be a violation of city Republicans’ civil rights, it appears unlikely that such a transfer would, at this point, be permissible.

A spokesman for the city’s Board of Elections, Christopher Riley, said a candidate cannot simply decline his petitions and designate them for another candidate. That is a role reserved to a candidate’s “committee to fill vacancies”: a group of at least three registered members of a candidate’s party selected by the candidate, and approved by petition signatories, to find a replacement if the candidate is unable to run.

Mr. Shaw said he had not designated such a committee on his petitions, and, despite an eleventh-hour attempt to form one before the Ognibene camp filed Mr. Shaw’s petitions, it appeared unlikely that Mr. Shaw would be able to bequeath stacks of Republicans’ signatures to his former rival.

Mr. Ognibene said, however, that he would still file the Shaw petitions as a “separate volume” to his own signatures.

“I still believe it’s a matter for the court to determine whether he has the authority to do it himself,” Mr. Ognibene said of Mr. Shaw’s wish to transfer the petitions without a committee to fill vacancies.

Meanwhile, Mr. Ognibene said he was not relying on Mr. Shaw’s petitions to get on the ballot and was proud of his own efforts.

“Shaw and I together getting close to 9,000 signatures is a far more impressive event than the mayor of the city of New York spending $30 million and getting 24,000 signatures,” he said.

Mr. Ognibene added that it was a sign of weakness on Mr. Bloomberg’s part that the Democratic candidates probably would far outstrip an incumbent mayor in their petition-circulating efforts. Indeed, the Democrat who ranks last in most polls, City Council Speaker Gifford Miller, obtained more than six times the mayor’s petition signatures, gathering around 158,000, according to his campaign.

The Democratic front-runner, Fernando Ferrer, placed second in the signature-gathering sweepstakes with around 100,000, a spokeswoman for his campaign, Christy Setzer, said. The Manhattan borough president, C. Virginia Fields, filed around 60,000 petition signatures, and a spokesman for the campaign of Rep. Anthony Weiner, Anson Kaye, said the congressman had obtained around 40,000 signatures.

Even if Mr. Ognibene fails to force a Republican primary, it appears he will nonetheless be a mayoral candidate in November. The chairman of the New York State Conservative Party, Michael Long, said Mr. Ognibene needed around 1,000 signatures to run on the Conservative Party line and he would be filing around 1,600.

“We’re in pretty good shape,” Mr. Long said.