ALBANY – With time running out before the end of session, an effort to lift the cap on the number of charter schools in the state has been resuscitated during negotiations between legislative leaders and Governor Pataki, sources said.

The emergence of charter schools as a dark horse in the flurry of last-minute bargaining here has come as a surprise to supporters of the schools, who had written off a victory this session and assumed the Legislature would take it up next year.

While those familiar with negotiations say the Democrat-controlled Assembly has not softened its opposition to an expansion of the schools, sources say charter schools could play a key role in a complicated end-of-session compromise made up of many parts and involving billions of dollars.

“It’s being discussed as part of the negotiations, and the ball is in the air,” a legislative source said.

Breathing life into the schools is Mr. Pataki, who is said to be hungry for a triumph on school choice, an issue that could be an important plank in his policy platform should he mount a campaign for president.

Mr. Pataki is focusing budget talks on charter schools, having secured a deal from lawmakers to expand the state’s criminal DNA databank, an issue he had been pressing hard in recent days.

The governor’s office refused to comment on the state of talks with legislative leaders. “The governor continues to push for an expansion of charter schools,” a spokesman for the governor’s budget division, Scott Reif, said last night.

Eight years ago, the governor scored his biggest victory on school choice when lawmakers permitted the state to establish charter schools, which are publicly financed, largely non-union, and exempt from many school district regulations. At the same time, they set a limit of 100. New York has 79 active charter schools, and the last 21 are set to open in the fall.

Mr. Pataki earlier in the year proposed raising the cap on the schools to 250 and lifting the limit for New York City, whose chancellor is one of the charter school movement’s biggest supporters.

The proposal received tepid support from Senate Republicans, whose highest priority this session has been securing property tax cuts for homeowners. Led by Speaker Sheldon Silver, who is an ally of the teachers’ unions, Assembly Democrats have stood in the way of Mr. Pataki’s plan.

This time around, a lift of the charter school cap may not be tied to pay raises, as some had suspected it would.

Instead, the governor is looking to exchange hundreds of millions of dollars in Medicaid spending for the Assembly’s blessing on the schools, sources said.

The deal would be part of a complicated budget clean-up bill that would also include money for a number of capital projects both upstate and in New York City.

The governor has said he has constitutional problems with about $650 million in Medicaid spending approved by the Legislature. Much of the money was supposed to fund higher reimbursement rates for hospitals and nursing homes, but the governor argued that lawmakers appropriated it in an illegal manner and vowed not to spend it.

Sources said the Republican Senate majority leader, Joseph Bruno, is also pushing for more charter schools, an issue he shied away from during budget negotiations earlier in the session. The majority leader has a good reason to push for an expansion: He would like Mr. Pataki to sign off on a property tax bill that would give state-funded rebates to homeowners.

Mr. Silver has never ruled out an expansion of the schools, which have some support within the Assembly’s black and Latino caucus. While Mr. Silver in recent public comments said the schools were not being discussed, lawmakers have said they suspected that the speaker was withholding his support for the purposes of using it as a bargaining chip during end-of-session negotiations.

“It’s my understanding that the governor is attempting to keep it in the mix,” a Democratic assemblyman of Buffalo, Sam Hoyt, said. “The Assembly’s position has not changed.”

The Assembly last month took up the issue in conference meetings but dropped it after school choice groups ran advertisements attacking lawmakers who are opposed to the schools. Mr. Silver threatened to cut off the debate entirely unless the ads stopped running.