A spruced-up, tuition tax credits bill expected to be made public today will extend credits to families whose kids already are in private schools, the sponsor said Tuesday.

That group has been left out of past bills because giving them a credit would yank tens of millions of dollars out of public school coffers, which rely on income tax revenues, analysts have said.

But Rep. Jim Ferrin, R-Orem, believes he's found a way to make it work. His Substitute HB39 would scale credits to benefit the poor. Lower-income residents would get $3,750; wealthier families, $500.

"Arguably many students in private schools today aren't going to qualify for the credit anyway because of their higher economic status," Ferrin said. "But (the provision) could change," depending on the fiscal analysis.

Extending the credit to current private school families also could calm constitutional concerns over favoring one group over another. But they took a potential co-sponsor by surprise.

"My initial reaction to that is concern," said Rep. Steve Mascaro, R-West Jordan.

All eyes now will turn to the Legislative Fiscal Analyst's Office to determine the substitute bill's impacts on the public school system. Will it cost the state money, as school officials claim, or save it by enticing people to remove kids from growing public schools with the state picking up just part of the tab?

The bill is expected to be one of the biggest political, philosophical and financial fights of the 2005 Legislature.

Ferrin and Mascaro last week were putting finishing touches on the substitute bill. Their collaboration — Mascaro has requested a competing bill — could prevent further splitting already divided House Republicans, who have held up the bill for years.

HB39 seeks up to a $2,000 tax credit for people switching from public to private schools. People and businesses donating to a private school scholarship fund also would receive a credit.

Ferrin was putting final touches on a substitute bill Tuesday afternoon. He said changes will:

• Remove sections giving a credit for scholarship fund donations.

• Give $1.5 million in general — not school — funds to bail out public schools financially hurt by the credits.

• Mandate participating schools reveal teacher credentials and standardized test scores to parents.

• Require parents have students enrolled in private schools full time to participate and tell public schools if they don't plan to return the following year.

• Prevent home schools from participating.

Yet perhaps the most significant change is "means-testing" the credit to benefit the poor.