COLUMBIA - Schools, local governments and state-supported services could be in for trouble if Gov. Mark Sanford and GOP legislators lower the state income tax, economists said Monday.

Sanford and House Speaker David Wilkins, R-Greenville, are expected today to announce a proposal to lower the 7 percent income tax by a third, to 4.75 percent, in the next decade.

The tax would be cut incrementally only in years when the state's revenue increased 2 percent or more. No other taxes would be levied or raised to make up for the lost revenue.

Experts say South Carolina is the only state considering a tax cut without a corresponding tax increase. Economists predict the state would have to reduce services if it did that.

"Most people would not cut their income if they needed more money," said David Brunori, a George Washington University tax law professor and a contributing editor to the tax policy publication State Tax Notes.

Local governments don't directly receive money from the income tax. But leaders worry the state will cut local funding - especially to schools.

"We have been able to protect vital services with user-fee increases," said Richland County Council member Kit Smith. "We may be out of tricks."

Economists say the local officials have reason to worry.

South Carolina's budget has been in the same dire straits as other states for three years. This year, lawmakers must find about $350 million to balance the 2004-05 budget by raising taxes or cutting services.

States got into financial trouble after 2000, Brunori said, partly because they cut taxes during good economic times.

When states develop a deficit, he said, one of the first things cut is aid to local governments, forcing cities and counties to raise property taxes to make up the money.

"The net effect is - I don't want to say disastrous, but it's pretty severe," Brunori said.

Republican legislators who support the Sanford-Wilkins plan say the tax cut would stimulate the economy.

But economists and tax experts said they have not seen proof that the tax base would grow enough to pay for services.

"You're, in essence, arguing supply-side economics at the state level, and I'm not convinced that works," said Harry Miley, chairman of the state Board of Economic Advisors under former Republican Gov. Carroll Campbell.

"Are [enough] people going to move to South Carolina because the tax rate decreases? I don't know the answer."

Sanford's spokesman said he could not comment until after today's news conference unveiling the tax proposal. Wilkins also declined to comment.

Sanford said during his campaign and in the past that income-tax relief has effectively stimulated the economy in states that have tried it.

But economists Monday said they could not name a state cutting income taxes now - without increasing another tax to make up for the lost revenue - on the tail end of a recession.