RALEIGH, N.C. - Two years ago, the North Carolina legislature put a cap on the state fuel tax.

While drivers currently save about a nickel for each gallon they buy because of the cap, the total loss to the state Transportation Department is much greater: $600 million.

That's about how much less the department will have taken in cumulatively by the time the cap is scheduled to expire June 30, compared to the amount that would have been collected had there been no cap, according to state estimates.

Department and General Assembly researchers estimate more than half of the money would have been collected this fiscal year, when record gas prices combined with the states variable fuel tax formula would have brought in more than $400 million extra.

The state warned last month that if tax revenue stays at the current level, the department will be forced to cut $200 million by next summer. Greater shortfalls will prompt even deeper cuts.

Lawmakers returning to Raleigh next month must decide whether to let the cap expire or extend it and find money elsewhere to pay for road construction and repair. There's an estimated $65 billion gap between transportation revenues and needs in North Carolina through 2030, the Department of Transportation has said.

In the past, North Carolinas fuel has automatically adjusted twice annually based on the average wholesale price of a gallon. The adjustments, based on a six-month average for fuel, were designed to keep the taxs value from eroding.

The legislature agreed to limit the tax to no more than 29.9 cents per gallon starting in mid-2006 after complaints when it rose by roughly 3 cents because gas prices had surged in the aftermath of Hurricanes Katrina and Rita. Gov. Mike Easley initially was cool to it but later signed a budget bill with the cap.

Without the cap, the legislature's Fiscal Research Division says the tax now would have been 34.8 cents per gallon and soared to 41 cents the first of next year.