COLUMBIA - Gov. Mark Sanford's plans for tax credits to cover private school tuition could undermine public education in a funding system that already is discriminatory, U.S. Sen. Lindsey Graham says.

Graham is one of Sanford's top political allies, but the two Republicans don't agree on how to accomplish one of Sanford's top legislative goals.

Sanford's proposal would give parents credits on a variety of state and local taxes to offset private school tuition. The governor has said that will inject competition into the public education system.

Graham told members of the Association of Capitol Reporters and Editors recently that the state's system of funding public education is "inherently discriminatory."

That issue is raised in a school funding lawsuit brought by eight rural school districts around the state.

Parents and others in the case say students in the poor districts start off disadvantaged because the state does not adequately fund their schools.

The Circuit Court case has been working its way through the judicial system for years and it could be two years before the arguments and appeals end.

Graham expects the plaintiffs will lose, but that doesn't mean a change is not needed.

"If I had a child in a school district that was chronically underfunded because the funding mechanism was inherently flawed ... I would complain, I would go to court," he said.

With schools largely financed through property taxes, "we have regions of the state that are always going to be left behind," Graham said.

Yet, Sanford's plan for tax credits may not be the right approach, he said.

"Going to private schools with public money -- I'm not too sure about that," Graham said. "That does, I think, undermine public education in the long term."

Graham told The State newspaper Thursday that he was not criticizing Sanford's tax credit proposal, but he warned it may be promising more than the constitution will allow.

"Mark and I absolutely see the same problem and share the same goals: infusing school systems with new money and new reforms," Graham said.

While some argue Sanford's plan would raise constitutional challenges of public money going to private schools, supporters say tax credits are not public money.

Graham said he is considering legislation that would create a federal program to help states or local districts match federal money to pay for assistance programs.

Sanford's plan died in the House earlier this year, and budget estimates showed it would have cost the state $234.4 million plus $37.8 million in local property taxes.

Had it been fully implemented by 2010, 73,000 students were expected to take part.

Opponents have called the governor's proposal a "backdoor voucher program" that would cut public school spending.

However, Sanford spokesman Will Folks said it would increase per-pupil spending. That's because there would be fewer students in public schools benefiting from the same amount of state spending.

Sanford welcomes Graham's opinion, Folks said.

"We happen to think differently," Folks said of the issue of using tax credits for church-run schools. "But that's what this process is about -- we exchange ideas. Ultimately there's a resolution."