COLUMBIA - Gov. Mark Sanford's plans to cut the state's gasoline tax could threaten the state's credit rating, cut money for projects in the works and reduce the amount the state could borrow to build and repair roads and bridges, according to lawyers the state pays to look out for bonds it issues.

Sanford spokesman Joel Sawyer says the governor's office disagrees with the bond lawyers. They "are paid to read the law in what some would say is an overly restrictive way," he said.

On May 10, Sanford proposed a Memorial Day-to-Labor Day suspension of the 16.8 cent-a-gallon tax, saying residents and tourists could use the $134 million it generates to offset prices at the pump.

Later that day, the House approved a gas-tax break for October, November and December, but that is expected to die today. It's not part of the compromise plan a budget conference committee is expected to send to the House and Senate for approval this week.

Sanford and the House would have made up for the gas-tax break with surpluses generated from faster-than-expected revenue growth. That's important because most of the gas-tax money is linked to debt repayment.

For instance, the equivalent of a penny-a-gallon goes to the South Carolina Transportation Infrastructure Bank to help repay $1.9 billion in outstanding bonds.

The state has contracts with bondholders spelling out how those revenue bonds are to be repaid, said Wayne Corley, a McNair Law Firm lawyer in Columbia representing the bank. The debt repayment plan is a factor in the risk rating the bonds have.

"If such revenues are not available to the SCTIB for payment of its revenue bonds, it may have a negative impact on such ratings," Corley wrote in a letter to Senate Finance Committee Chairman Hugh Leatherman, R-Florence. The Legislature, Corley wrote, "may not enact legislation which would impair the rights created under this existing contract."

The state has been fretting credit ratings for more than a year. Last summer, Standard & Poor's Ratings Services lowered the state's AAA credit rating to AA-plus. That sparked a political blame game that's carried over into this election year.

There are other concerns.

Limits on borrowing are set by the constitution. Because of that, losing gas-tax collection for three months could affect the state's borrowing capacity, according to a May 17 letter to Leatherman from Eric Shytle, a lawyer for Haynsworth Sinkler Boyd in Columbia and the state's bond counsel.

And "it could affect the security for and payment of highway bonds already issued and outstanding," the bond lawyer wrote.

Leatherman says money earmarked to repay a bond debt needs to be used for that purpose.

That's the same kind of argument Sanford used as he admonished legislators to repay money raided from trust and reserve accounts. When legislators argued that some of the accounts actually weren't reserve accounts, Sanford countered that they should restore the raided money and then argue about what was a reserve account.

Sawyer said he hoped Leatherman's request wasn't "an excuse not to provide gas-tax relief to the people of South Carolina."

With the state projected to take in nearly $1 billion dollars more in the 2007 fiscal year than in the 2006 fiscal year, "we don't see any reason not to provide tax relief for the people of South Carolina."