Proponents of an education tax credit have spent more than half a million dollars on a direct mail campaign aimed at giving the measure a boost in Albany as the Senate, Assembly, and Governor Pataki enter the crucial final week of budget negotiations.

Teach NYS, a three-month-old lobby based in Brooklyn that is primarily backed by Catholic and Jewish groups and philanthropists, sponsored the nearly million-piece campaign, unusual for a legislative measure in New York State. The group is seeking to chip away at the teachers unions’ sway over state education policy.

Supporters of Mr. Pataki’s tax credit proposal, which would give parents in New York a refundable tax credit of up to $500 a dependent for private school tuition and tutoring, say the money for the most part would go to families with children in public schools and would encourage parents to spend money on their children’s education.

After months of intense lobbying, the proponents of education tax credits are likely to come up short when the final budget is decided. But the group’s efforts have helped drive the issue to the forefront of Albany’s agenda this winter and have introduced to the Capitol a fledgling but growing interest group: parents of schoolchildren.

One glossy mailing sent by Teach NYS to thousands of residents says, “Education Tax Credits will send money back to lower and middle income families for” various educational expenses, including items such as textbooks and software that aren’t listed as qualified expenses under the governor’s plan. The mailing asks the recipient to contact the state Assembly and Senate, stating, “You have only a few precious days left to keep education tax credits … call today.”

The mailing was one of several campaigns conducted by Teach NYS. They have ranged from 60,000 to 200,000 pieces at a cost of about 50 cents a piece. One of those mailings was targeted at the Assembly district of the Democratic speaker, Sheldon Silver, who, in the face of pressure from the teachers unions, has come out against a tax credit that would be linked to tuition expenses.

“We’ve done an astronomical amount of mailings,” the executive director of the Sephardic Community Federation and a member of the lobby’s board of directors, David Greenfield, said.

The mailing has been coupled with a print advertising campaign in about a dozen newspapers, such as the New York Observer in Manhattan, and the Journal News, a Gannett newspaper in Westchester, Rockland, and Putnam counties.

The executive director of Teach NYS, Michael Tobman, who previously was director of intergovernmental affairs for Senator Schumer, said one of the purposes of the campaign was to “counter efforts by tax credit opponents to mischaracterize the efforts.”

The state and city teachers unions, which are among the most post powerful interest groups in Albany, have lobbied aggressively against the tax credits, which they have characterized as a tuition voucher that would take hundreds of millions of dollars from public education. The unions have had their own print campaigns and set up phone banks of volunteers to call members and ask them to tell lawmakers about their opposition to education tax credits. The unions also warned lawmakers that they will cut off campaign contributions if they back the measure.

Lawmakers who support the credits and officials at the governor’s office have said the program proposed by Mr. Pataki isn’t taking away money from public education, which is likely to receive a funding increase this year of a record $1.1 billion.

While the unions say they would support a general tax credit, such as the one that has been proposed by the Democratic-controlled Assembly as an alternative to the governor’s plan, they are pressuring lawmakers not to support any measure that would include tax breaks geared to families that spend money on private schools.

By associating the tax credit proposal to vouchers, the union is seeking to connect the measure to a major plank of the school choice movement and thus cast the tax credits in an ideological light.

In a number of states, courts have struck down vouchers as unconstitutional because they were found to be in violation of provisions in state constitutions barring direct government aid to religious institutions. Education tax credits, which indirectly support religious schools, have survived court challenges in states like Minnesota, Arizona, and Illinois.

Yesterday, lawmakers in both houses had yet to agree on a wording for a tax credit bill. The Senate version restricts the tax relief to parents with children who are enrolled in school but it does not require that parents use the credits, which could total as much as $333, for educational expenses. All three versions, the Assembly’s, Senate’s, and the governor’s, cost about $400 million.

Mr. Pataki has said education tax credits are one of his four highest priorities during this budget season, and he has not ruled out vetoing a budget that does not include them.