The Sonoma County Board of Supervisors on Tuesday endorsed a plan to increase the network of county roads designated for long-term maintenance by 63 miles, about 5 percent of the 1,382-mile network.

The move, which requires formal adoption at a later date, would bring the county's so-called priority road network — the routes identified for long-term maintenance because of their federal funding or importance for regional travel — to 219 miles, roughly 16 percent of the total network.

The added miles — representing 39 roads — include a 5.4-mile stretch of Bennett Valley Road from Grange Road to Warm Springs Road, a stretch that Bennett Valley residents lobbied to have restored to the priority network.

Other major segments to be added include 8.2 miles of Valley Ford Road from Highway 1 to Tomales Road and 6.1 miles of Graton Road from Bohemian Highway to Highway 116.

Most of the segments are in good shape now, and the aim is to focus long-term maintenance efforts on them to keep them that way, said Phil Demery, director of the county's Transportation and Public Works Department, which prepared the plan.

"This is to keep the good roads good," he said Tuesday.

The plan comes as a sequel to the supervisors' decision last October to designate 150 miles of heavily traveled roads for pavement preservation, the county's label for long-term maintenance that includes sealing and resurfacing as needed.

In August, six miles of road were added to the list.

The plan is driven by maintenance costs that officials said far exceed the county's share of federal and state gas tax revenue, the main source of funding for road upkeep. Property tax revenue, by contrast, provides just half a cent of every dollar for road funding.

The gas tax revenue formulas are based on the volume of fuel pumped and they have not changed since the early 1990s, county officials said. They also tend to favor more urban areas, they said.

"Even in good economic times, our funding was inadequate," Demery said Tuesday. "This problem began 20 years ago and it's progressively gotten worse."

Supervisors agreed on Tuesday to send a letter to transportation officials lobbying for a change in the revenue allocation.

Going forward, all county roads not on the priority list — currently more than 1,200 miles — would still qualify for some maintenance, including pothole repair, debris removal, drainage ditch clearance and bridge maintenance. But without further pavement work those roads likely will crumble and would have to be turned to gravel in the long term, public works officials said.

The additional 63 miles of priority roads would require doubling the amount the county currently spends on pavement preservation. The new figure would be $9 million.

Supervisors agreed to study several ways to cover those costs. The board endorsed a proposal to divert up to $2.2 million a year in solid waste franchise fees collected from garbage haulers and to look at increasing the hotel bed tax, a move that could generate up to $2.5 million.

They also agreed to study cost-cutting proposals, including a reduction in brush clearing along roadsides — a service that currently costs the county $3.3 million a year — and a shift in ownership and upkeep of some dead-end roads to private landowners.

The board is set to resume its discussion of the issue early next year and adopt a plan before the start of the next fiscal year in July.