CANTON — St. Lawrence County's plan to tackle fuel overruns centers on an unused fund set aside for environmental cleanup projects.

The county has exhausted the $650,000 it gave the Highway Department for fuel and diesel. Staff will present a plan Monday that injects $300,000 from the environmental fund created in November and fees from registering vehicles for downstate auto dealers.

The environmental fund would be docked $100,000.

It has not been used as intended. It lingered while legislators debated which properties and expenses should receive priority. Legislator Peter W. FitzRandolph, D-Canton, predicted at the time that it would be one of the first places raided during tight fiscal times.

Legislature Vice Chairman Frederick S. Morrill, D-DeKalb, was the driving force behind the environmental fund. He had to be convinced by County Treasurer Robert O. McNeil that taking some out for fuel was a good idea.

"At first I told him, 'No, absolutely not,'" Mr. Morrill said. "Then I had to put my financial hat on and say, 'This is the responsible thing to do.'"

Mr. Morrill, an accountant, was convinced because staff selecting which properties to tackle have not settled on a plan and are unlikely to spend the entire $323,101 this year. It also can be replenished from annual delinquent-tax property auctions.

The remaining $200,000 for fuel will come from fees charged under County Clerk Patricia A. Ritchie's effort to solicit business from New York City auto dealers. The clerk's office keeps 12.7 percent of all DMV transactions, and Mrs. Ritchie's active pursuit of dealers has netted the county more than $300,000 since 2006. That money has been going into the county's general fund.

Highway Superintendent William E. Dashnaw estimated in late June that the department will need about $500,000 for the year's remaining fuel purchases. Legislators will decide Monday on the $300,000.

"The idea is to wait and see if sales tax comes in higher and how the departments are performing," Mr. Morrill said.