A pilot tuition tax credit program approved by a House panel last week would cost the state half a billion dollars in one year, according to a study by the state Board of Economic Advisors.

The report, released Tuesday, left many lawmakers certain the pilot program would fail when it hits the House floor — possibly as early as today.

“I cannot imagine the (full House) will support it,” said Rep. Adam Taylor, R-Laurens, who wrote the amendment to scale back Gov. Mark Sanford’s tuition tax credit proposal from a statewide program to a test for two school districts.

The bill also would have given tax credits to people who donated to public and private schools.

Many lawmakers said they were already leaning against the pilot program before the cost estimate was released. They support other options — including killing the bill outright.

The study gives supporters and opponents more fodder to argue for or against tax credits, lawmakers on both sides said.

According to the Board of Economic Advisors, the pilot alone would cost about $16 million by 2007-08, when it would be fully phased in.

The state would lose another $500 million if taxpayers were allowed to donate what they owe in taxes to public schools, the BEA found.

The BEA previously estimated a statewide tuition tax credit program — without tax credits for public school donations — would cost $500 million over five years.

Lawmakers already concerned about what tuition tax credits might do to the budget were more worried after seeing the pilot’s estimated price tag.

“We can’t just go in and blindly say we’re going to pass this initiative,” said Rep. Michael Thompson, R-Anderson. “We’ve got to say how we will find the money in the budget.”

Most lawmakers are focused on two other options.

Opponents want to kill the bill, which they say would hurt public schools and siphon money from other state programs. Rep. James Smith, D-Richland, said a bipartisan group of lawmakers will vote against the tax credits.

“This whole effort is completely irrelevant to the clear work we need to do to improve education in the state,” Smith said.

Many tax credit supporters are rallying around a plan that would offer tax credits or vouchers to children in failing schools.

Vouchers would allow low-income parents to pay private school or other school expenses with money that would have gone to public schools.

Other parents would get tax credits to pay for private school tuition, home schooling or to transfer their children to another public school.

Sanford supports this option and is lobbying House members to get their support, spokesman Will Folks said.

The children who would be helped “are the most at-risk kids,” Folks said. “This is where the real change needs to occur.”

Rep. Ted Pitts, R-Lexington, who opposed Sanford’s original statewide proposal, now says he likely will support the plan that would target failing schools.

Pitts disliked Sanford’s plan because it allowed anyone to donate to scholarships what they owed in taxes. That could have disastrous effects on the state budget, he said.

Reach Talhelm at (803) 771-8339 or jtalhelm@thestate.com.