A showdown between two Republican heavyweights over the right to run for the seat in the 59th State Senate District may unfold at a meeting of Erie County Republicans tonight in Pettibone’s Grill amid a growing divide between supporters of James P. Domagalski, chairman of the county GOP, and former Sheriff Patrick Gallivan.

While Domagalski on Tuesday joined former East Aurora Mayor David J. DiPietro as officially declared Republican candidates, Gallivan and Lancaster Mayor William G. Cansdale Jr. are seriously considering joining the contest to succeed retiring Sen. Dale M. Volker, R-Depew.

But even though Domagalski plans to relinquish the GOP chairmanship tonight in order to run, most observers say Gallivan faces a Herculean task to postpone tonight’s scheduled endorsement vote, since Domagalski still has enormous clout over the county Republican committee.

“There will be a request for a one-week postponement in the voting,” said one Gallivan supporter who asked not to be identified.

“I don’t see a situation where that is going to happen,” countered a pro-Domagalski source.

Gallivan, a state Parole Board commissioner who before serving as sheriff was a captain in the State Police, was involved in hearings all day Tuesday and was unavailable to comment.

But supporters say he is being encouraged to run by top Republicans such as Volker and former Rep. Thomas M. Reynolds of Clarence. Nobody has said Gallivan is ready to declare his candidacy, but friends say that his family is supportive and that he already has begun to line up campaign staff.

“My impression is that he is taking an extremely serious look at it,” said another Gallivan confidante, who asked to remain anonymous.

Other sources say that Gallivan would have to resign his $101,600 job with the Parole Board and that efforts are under way to find an interim position to support him during the upcoming campaign.

But Gallivan also faces a proposal in Gov. David A. Paterson’s new budget that would cut six of the Parole Board’s 19 members, a move that, if approved by the Legislature, could immediately affect him.

Gallivan’s sudden interest in the Senate played out against Domagalski’s official announcement of his candidacy Tuesday in the atrium of the Hyatt Regency Buffalo. The outgoing chairman gathered some of the top names in local Republican politics to underscore his core support and repeated his now-familiar mantras about private-sector “citizen legislators” reforming the ways of Albany.

But he also took a swipe at DiPietro, a “tea party” activist who is already attacking Domagalski. “All they’re going to be for is being mad,” Domagalski said. “I’m talking about Mr. DiPietro and the negativity.”

The former mayor earlier this week lashed out at Domagalski for “smoked-filled- room maneuvering,” while labeling him a “vanity candidate” who forced Volker from the Legislature.

“It’s an open secret that Domagalski considers Volker’s Senate seat his own personal property, so when Dale was still running, Jim stabbed his old friend in the back to satisfy his personal ambition and power lust,” DiPietro said.

Several party sources say Gallivan’s possible candidacy is fueled by resentment among Volker loyalists at Domagalski’s threat of a primary against the 38-year incumbent.

At the same time, some of those loyalists also privately believed it was time for the senator to retire.

Domagalski praised Volker in his Tuesday remarks but reiterated his claim that all of Albany needs to be revamped.

“It’s time in Albany, for Republicans and Democrats alike, to have a significant sea change from where we are,” he said. “It’s not us that’s saying it; it’s the voters saying it. The time has come for a new and different approach.”

But no internal rancor was evident at Domagalski’s announcement. Those lining up behind him included incoming Erie County Republican Chairman Nicholas A. Langworthy, former State Attorney General Dennis C. Vacco, former Erie County Comptroller Nancy A. Naples, former Ambassador Anthony H. Gioia and Erie County Conservative Chairman Ralph C. Lorigo.

And in a sign that important factions of the party are united behind Domagalski, County Executive Chris Collins’ chief of staff, Christopher M. Grant, also attended, as did a group of Board of Elections employees.

Domagalski’s most significant supporter attending the event may have been Republican gubernatorial hopeful Carl P. Paladino, who more and more appears to be Erie County’s choice for governor this year.

“He is a young, vibrant, intelligent and honest human being,” Paladino said of Domagalski. “And he is willing to take on this silly system in Albany. I’m highly supportive of anyone like that.”

Domagalski also said he is an “unabashed supporter” of the Unshackle Upstate program advanced by the Buffalo Niagara Partnership and other economic development groups, which already is raising substantial dollars to be funneled to Republican Senate candidates this year.

His Tuesday event displayed all the trappings of a full-fledged candidacy, including signs, buttons and the presence of a Republican media consultant, Matt Dabrowski.