The increasing likelihood that the next majority leader of the Senate will be the Queens Democrat Malcolm Smith, a founder of two charter schools whose pastor and political mentor is a vocal school voucher supporter, is exciting school choice advocates across the state.

Senator Bruno, the Republican Senate majority leader who just announced he will not seek re-election, is a supporter of charter schools, but Democrats such as Mr. Smith have been a rarer breed.

Mr. Smith has championed efforts to lift the state’s charter school cap and has also embraced the idea of tax breaks for parents with children at private schools. The positions have given him an unusual pedigree of cheerleaders and contributors; in addition to the usual list of lobbyists and real estate developers, Mr. Smith is supported by people such as the money manager Ravenel Boykin Curry IV, a founder of the lobbying group Democrats for Education Reform who first became enamored of Mr. Smith at a dinner four years ago at Mr. Curry’s apartment overlooking Central Park South.

There is just one catch for some activists: Although Mr. Smith’s support for charter schools and tax credits has been consistent, some are worrying that if he ascends to the Senate’s top leadership position, he might not deliver on the promises or that his posture could change.

The dilemma as Mr. Smith rises in prominence was perhaps exemplified last year when Mr. Curry’s group, which has stood against the teachers union by strongly promoting charter schools, hosted a fund-raising dinner for Mr. Smith at Mr. Curry’s apartment — only to learn that the president of the United Federation of Teachers, Randi Weingarten, was holding her own fund-raiser for Mr. Smith the next day.

Since becoming minority leader of the Senate, Mr. Smith has also resigned from his positions on the boards of two charter schools he helped found.

And eyebrows were raised when a charter school on whose board Mr. Smith once served, the Merrick Academy in Queens, approved a move by its teaching staff to unionize.

In an interview yesterday, Ms. Weingarten said Mr. Smith played a critical role in helping Merrick Academy unionize. She said that since Mr. Smith became minority leader, he has said he is not beholden to the school-choice agenda, even though it may be his “personal ideology.”

Formerly a businessman who built “affordable” housing in Queens, Mr. Smith’s political pedigree arcs back to before his business days, when he served as a top political aide to the Reverend Floyd Flake, then a Democratic congressman.

Rev. Flake, who runs a Christian school out of his church, the Greater Allen African Methodist Episcopal Cathedral, is a vocal supporter of school vouchers, and Mr. Smith is a close friend and loyal member of the church — like “family,” Rev. Flake said.

The senator attends services every Sunday that he is not in Albany, appearing punctually at the early 6:30 a.m. service. He has also sent his two children to the school, and Rev. Flake’s son is now Mr. Smith’s advance man, Rev. Flake said.

Ms. Weingarten said the senator is being careful not to promote his own ideology but rather the philosophy of his caucus and the will of the people. She added that she has been having “plenty of conversations” with Mr. Smith recently. “This may quite surprise the school-choice people,” she added. “And he’s asked me to work with him closely.”

In school-choice circles, the moves by Mr. Smith are causing some quiet anxiety.

“Part of what has made Senator Smith authentic and genuine has been his willingness to lead on issues, like public charter schools and education tax credits, which have been traditionally difficult for Democrats,” the lobbyist Michael Tobman said. “The worry now is that he’ll abandon that which has brought him success in favor of having an easier time with entrenched interests.”

Other supporters said they are confident that, if the Democrats take the Senate and Mr. Smith becomes majority leader, he would stand up to the test of leadership.

Mr. Curry said his confidence in Mr. Smith has been strong ever since he hosted the state Senator and Governor Paterson, then a state Senator as well, for dinner at his apartment. The men spoke for four hours about the importance of transforming public education, and Mr. Curry emerged a believer in Messrs. Smith and Paterson.

“It was completely different from all my notions of Albany as filled with political hacks who only cared about getting re-elected,” Mr. Curry said yesterday. “Immediately, our group started supporting Malcolm and David because they were the only Democratic senators who were brave enough to support charter schools and real education reform.”

Mr. Curry said his confidence is only growing now, as the growing number of charter schools in the city turns support of them into a political asset.

The Harlem charter-school operator Eva Moskowitz, a Democrat who used to chair the City Council’s education committee before the teachers union worked to defeat her in a run for president of Manhattan, praised Mr. Smith for his support of charter schools.

But she said that he should accelerate his support. “To keep pace with parents, Democratic leadership will need to be even bolder and be unafraid to clear the obstacles to reform,” Ms. Moskowitz said.

Mr. Smith’s office did not return several requests for comment.