ANNAPOLIS -- Maryland is bracing for the potential loss of one-third of its federal transportation funding, forcing the state to slow down work on $4 billion in mass transit projects while lawmakers consider raising taxes and fees to meet the state's needs.

Under a six-year transportation spending proposal supported by the U.S. House, Maryland would lose 35 percent -- or roughly $170 million annually -- of its federal aid for the construction and maintenance of highways, roads and mass transit systems, analysts told a state Senate budget panel on Wednesday.

Maryland lawmakers would have to raise the state's 23.5-cent-per-gallon gasoline tax by roughly 6 cents to account for that loss, according to Jonathan Martin, an analyst with the Maryland Department of Legislative Services.

The state is counting on even more federal money to help build the 16-mile Purple Line -- a rail connecting New Carrollton to Bethesda -- and extend Baltimore's Red Line. Maryland has already invested tens of millions of dollars in the planning phase of the projects, and the state was expecting to secure about $2 billion from the federal government before breaking ground, Maryland Transportation Secretary Beverley Swaim-Staley said.

"We need to have the federal commitment before we could engage in those projects," Swaim-Staley said. "If we don't have the funding ... the best we could do for now ... is at least keep [the projects] in the pipeline."

Compounding the federal funding uncertainty is a $12 billion backlog in local transportation needs and a thinning stream of revenues from the state's gas tax, Swaim-Staley said.

"Even if we had the federal government fix their issue and we fix the state issue, we're not going to be able to [address] a backlog of $12 billion in [local transportation needs]," she warned.

Gov. Martin O'Malley has raided more than $700 million over the past three years from local governments' share of transportation funding to help plug annual state budget deficits. As a result, local governments are now sharing $148 million to repair and maintain roads and bridges, compared with the $467 million they shared in fiscal 2009.

The Senate Budget and Taxation Committee on Wednesday discussed a range of options for replenishing transportation funding, which included increasing the state's gas tax, imposing a sales tax on gas, giving local governments the authority to raise various transportation-related taxes, and raising tolls and fees.