The head of the state’s Conservative Party called one of Mayor Bloomberg’s Republican challengers the “odds-on favorite” for the organization’s endorsement in November’s mayoral election.

The party chairman, Michael Long, told The New York Sun that the former Republican minority leader of the City Council, Thomas Ognibene, seemed to have the best shot at the Conservative endorsement.

“From what I understand, I think the county leaders are going to wind up on the same page,” Mr. Long said Monday during a telephone interview. “They haven’t made their decision and the process is still going on, but I would think Ognibene is the odds-on favorite.”

The impending endorsement would mean that even if Mr. Bloomberg defeats Mr. Ognibene as well as another challenger, Steven Shaw, an investment banker, in a GOP primary – which polls suggest he will do handily – the Queens politician could still pose a problem for the mayor in the general election.

Political experts said Mr. Bloomberg needs all of the conservative votes he can scrape together in the general election to beat a Democratic opponent. A formidable candidate on the Conservative line could siphon away thousands of those votes.

“Michael Bloomberg would certainly be rather a more marginal candidate than Tom Ognibene, should he not get the Conservative Party line himself,” a Democratic political consultant, Scott Levenson, said. “I don’t think it’s just the fact that Bloomberg doesn’t have the line again. It’s that Tom Ognibene being on the line will add gravitas to it.”

In the 2001 mayoral election, the Conservative Party backed an attorney from Queens named Terrance Gray. While Mr. Gray won only 3,577 votes citywide on that line, Mr. Long said he expected this year’s party candidate to rake in far more support. He attributed the low numbers in the last mayoral election in part to post-September 11 concerns. In last November’s presidential election, the Bush-Cheney ticket won 26,463 votes on the Conservative line.

Party leaders in all five boroughs, Mr. Long said, are meeting with Mr. Ognibene and with Mr. Shaw, who is also seeking Conservative Party support.

Mr. Bloomberg has been criticized by many rank-and-file Republicans who say his tax hikes and other policy positions are not in line with their views. Mr. Ognibene, who rose through the ranks of the Conservative Party before finding his way to the Republican Party, has been highly critical of the mayor for the same reasons.

Yesterday, Mr. Ognibene said the first vote he ever cast was on the Conservative Party line, for Barry Goldwater in the 1964 presidential election.

Mr. Ognibene said that he hadn’t officially heard anything from the party, but that his interviews went well. He said he was not concerned about jeopardizing the race for Mr. Bloomberg, a Republican, if he ran on the Conservative line.

“Why would I be concerned about siphoning votes from the mayor?” Mr. Ognibene said. “I consider Mayor Bloomberg to be further to the left than some of the Democratic opponents. I don’t see him as a Republican.” He also took issue with Mr. Bloomberg’s indication the other night that he would support Senator Clinton, a Democrat, for re-election.

Mr. Levenson predicted that if the Ognibene endorsement comes through, the Bloomberg administation will have a problem on its hands.

“The margin of victory for Bloomberg in 2001,” he said, “was 30 or 40 thousand votes.”