ALBANY — In a victory for Governor Spitzer, lawmakers are poised to approve an expansion in the number of charter schools in the state, agreeing to give second life to an 8-year-old experiment in education that has been lauded by school-choice activists but resisted by state teachers unions and school district bureaucracies.

In one of last deals made during the budget negotiations, lawmakers have agreed to allow an additional 100 charter schools in the state, which would increase the total number of the schools to 200.

The trustees of the State University of New York, which are appointed by the governor, and the Board of Regents, a state entity largely controlled by Assembly Democrats, will each have approval power over 50 of the charters, which are publicly funded schools under contract with state entities but independent of school district bureaucracy and union rules.

The final budget will likely eliminate Mr. Spitzer’s plan to give parents who pay for private or public school tuition annual $1,000 tax deductions to offset the costs. Worth on average $68 a year, the money would have covered just a tiny fraction of tuition costs at most schools. For private and religious school advocates, the deduction represented a critical precedent for using state funds explicitly to help families pay for private tuition.

School-choice activists also supported the deduction plan as a small first step toward an approval of tuition vouchers or education tax credits that would increase competition in the state’s public school system.

Sources said Mr. Spitzer was still fighting to keep the deduction in the budget but was facing stiff resistance from the speaker of the Assembly, Sheldon Silver.

The deal marked the first approved expansion of charter schools since the Legislature first authorized 100 schools in December 1998 during the Pataki administration. The last of the 100 schools opened in the fall, with plans to open new ones frozen and thousands of students left on waiting lists. In his last year as governor, Mr. Pataki sought to lift the cap on the schools, but was blocked by Assembly Democrats.

Mr. Spitzer had proposed adding 150 schools in his executive budget in January, but the Assembly, whose Democratic leadership has been critical of the schools, came back with a proposal that reduced the increase to 50 schools, reduced per-pupil funding for the schools by an estimated 20%, and required that charter schools be unionized if they exceed 250 students.

In the end, a compromise was reached by splitting the difference. Although many of the new schools will be located in New York City, the deal is something of a disappointment for the Bloomberg administration.

Under the governor’s original plan, the city’s schools chancellor, Joel Klein, was to have the ability to open 50 new schools without the final approval of the Board of Regents, whose members are appointed by the Legislature. In the final budget, Mr. Klein will not be given such authority.

Charter school supporters greeted the news of the expansion with some reservation, waiting for more details to emerge about new regulations imposed on the schools. Several sources said last night that the budget would not reduce funding for charter schools but would change the law so that new schools that exceed 250 students within two years of opening would automatically unionize.

In another key education issue for the city, lawmakers and Mr. Spitzer softened a demand by the Assembly that New York City lower its class-size average to the state median level over a four-year period, or risk losing billions of dollars in new funding.

Although the exact wording is still being worked out, sources said Mayor Bloomberg will not be strictly required to lower class size by that amount, but will be forced to demonstrate that he is decreasing the burden on teachers.

The deals on education were reached after the governor and legislative leaders met privately in Mr. Spitzer’s executive chamber for several hours yesterday in a last-minute attempt to bridge disagreements over spending and policy.

Mr. Spitzer and the leaders had announced a “conceptual framework” on Tuesday evening, but the agreement was filled with so many holes that legislative conference committees were unable to complete the rest of the budget. After a day of confusion on Wednesday, Mr. Spitzer called the leaders into his office early yesterday and went down a list of about 50 unresolved items.

At one point the five leaders went into Mr. Spitzer’s office and sat alone without any staff members to discuss what one participant described the most “sensitive” issues, including charter schools.

Mr. Silver, in an interview last night, said the budget would add $900 million to state funds above the governor’s proposed state funds budget of $83.6 billion. It’s likely that more spending will be added in supplemental budgets before the legislative session concludes at the end of June. The all-funds budget is still estimated at around $122 billion, an increase of $8.5 billion over current year spending.

The Spitzer administration also struck a compromise on taxes, agreeing to phase out a provision that allows banks to reduce their tax liability by investing in real estate investment trusts. Small banks would still be allowed to take advantage of the REITs under the compromise plan, which also includes tax reductions for manufacturers.

The budget also includes a $300 million plan to support stem cell research, which was opposed by the Catholic Church, and nanotechnology development in New York.

Several items were removed from Mr. Spitzer’s budget, including a provision that would increase the amount of money the state collects from bottle deposits and decrease what is kept by beverage companies.