ALBANY -- Senate Majority Leader Dean Skelos' tenure looks set to come to a close Monday, Republican sources said, while jockeying between his potential successors continued Sunday.

Skelos (R-Rockville Centre), charged last week with federal corruption, could voluntarily resign his leadership post or face an internal revolt when Senate Republicans begin a closed-door conference at 11 a.m. Monday that could last all day.

Both Sens. John Flanagan (R-East Northport) and John DeFrancisco (R-Syracuse) were trying to muster a majority of the 33-member Republican conference to take over as the state's top senator, with allies of each claiming enough support to win.

Flanagan and DeFrancisco met privately Sunday and despite a lengthy session held late into the night, they were unable to reach a resolution, said a Republican close to the issue. The goal of the talks was to keep the disciplined Senate Republican majority cohesive and in power despite the crisis of leadership created by the charges against Skelos.

Two Republican officials told Newsday that GOP senators were "near unanimous" in the view that Skelos had to leave his powerful leadership position. Another said Sunday that there was "no way" Skelos would still be conference leader by Tuesday.

Federal prosecutors charged Skelos, 67, and his son, Adam, 32, with extortion, soliciting bribes and conspiracy. Skelos allegedly used the power of his office to force an environmental company, Arizona-based AbTech, and a major real estate developer, Glenwood Management of New Hyde Park -- which also is a big GOP campaign contributor -- to hire Adam Skelos as a consultant and send title insurance work his way. All told, the senator compelled the companies to pay Adam $200,000 since 2011, investigators alleged. They said Skelos, in return, helped AbTech win a $12 million contract with Nassau County for storm water treatment and represented real estate interests in major legislation.

Skelos has said he and his son are innocent and that the criminal complaint lodged against him is "nothing more than a news release."

Rank-and-file members initially stood by Skelos, but his support rapidly eroded in the ensuing days -- especially after Democrats tried to force a no-confidence vote Wednesday.

Eight upstate GOP senators have called for him to step aside and one, Sen. Robert Ortt (R-Lockport), has said he would introduce a motion to call for a vote on Skelos, majority leader since 2011, if he doesn't step down.

Former Assembly Speaker Sheldon Silver witnessed a similar erosion of support when federal prosecutors arrested him in January on corruption charges. In less than a week, rank-and-file Democrats went from initially supportive to calling for his ouster. Silver at first refused to step down but eventually did when it became clear his colleagues would have voted him out otherwise.

But the math surrounding a leadership vote was easier in the Assembly, where Democrats control more than two-thirds of the seats. It's tougher in the 63-member State Senate, which has 32 Republicans and one Democrat, Brooklyn's Simcha Felder, who conferences with them.

If Skelos refuses to step down and resign his seat, as some have suggested, Republicans could potentially lose control of the chamber because Felder might rejoin the Democrats, putting them in the majority.

"He would never do that," one Republican official said Sunday of Skelos.

Another added: "Dean may be very defensive and trying to go down with a fight, but Dean doesn't strike me as a guy who makes threats" that would benefit Democrats.

Complicating matters is the absence of Deputy Majority Leader Thomas Libous (R-Binghamton), who is fighting cancer and isn't expected in Albany Monday. Libous faces corruption charges he lied to federal agents in a scheme to use his political pull to land a lucrative job for his son, who has pleaded guilty to tax fraud.