Montgomery County Executive Douglas M. Duncan's $1 billion plan to relieve congestion with new roads and transit projects hit its first snag this week as state lawmakers questioned whether they could pass all the tax and fee increases needed to pay for it.

One key element of the Democrat's transportation initiative -- a proposal to raise $261 million by tacking a local fee onto state vehicle registration charges -- could face serious opposition in the General Assembly, local legislators said.

Duncan aides also have had to trim their assumptions about other revenue they hoped would be available to underwrite the plan. Initial estimates showed the county's share of a 10-cent increase in Maryland's gas tax would bring in $18 million. New projections place it at just $6 million.

Even the largest local piece of funding, a 3-cent increase in the property tax rate that Duncan wanted to dedicate exclusively to his plan, could face resistance from advocates for schools and social programs. Every penny of increase in the property tax rate costs the average resident $25, and several interest groups have told council members that they deserve a cut of any new tax revenue.

"I'm not sure the pieces are falling into place," said Del. John A. Hurson (D-Montgomery), who supports Duncan's initiative.

"I think it's going to be hard to get funding for everything this year," agreed Sen. Jennie M. Forehand (D-Montgomery), another Duncan backer.

This week, several members of the county's legislative delegation questioned the feasibility of Duncan's proposed vehicle registration fee. The projected decline in gas tax revenue is forcing him to increase the amount he is seeking from registration fees from $50 to $70. That would be on top of the $76 that the state charges vehicle owners every other year.

Duncan, who breezed to a third term by promising to address the county's transportation problems and stacked the council with like-minded members, warned legislators that they oppose him at their political peril.

"If [the lawmakers] don't support these particular funding pieces, and don't have other ways for us to raise these revenues, then we can't do the program, and we're stuck in traffic and congestion," Duncan said.

"They saw what the voters did to members of the council who couldn't support solutions for traffic and congestion," he said. "Four years from now I wouldn't want to be in their shoes."

Council member Steven A. Silverman (D-At Large) said members have already started reaching the conclusion -- even if Duncan hasn't -- that other taxes may be needed to enable the county to pay for a massive transportation initiative during strained economic times.

Some ideas being discussed, Silverman said, include a cell phone tax, an increase in the local share of state income taxes, and additional energy taxes. There is also discussion of financing as much as a third of the intercounty connector by making it a toll road.

"We're going to be looking at all of those things as we try to address revenue shortfalls," Silverman said.

Duncan does have support in the legislature for his plan. House Ways and Means Chairman Sheila Ellis Hixson (D-Montgomery) and Del. Peter Franchot (D-Montgomery) said that they will advocate strongly for it and that they believe the obstacles can be overcome.

"We're going to have an empty cupboard and huge needs," Franchot said. "But Doug can be very persuasive."

One lingering unknown is how Gov.-elect Robert L. Ehrlich Jr. (R), will respond to the idea of an increase in the gas tax or to the attempt by Montgomery to piggyback its fee on top of the state vehicle registration charge.

Paul Schurick, Ehrlich's spokesman, said yesterday that the governor-elect has not reached any conclusions about the ideas. But Ehrlich remains supportive, Schurick said, of efforts to get moving on Montgomery County road projects.

Duncan unveiled his Go Montgomery program in June, and it quickly became the centerpiece of his reelection campaign. The plan calls for $1 billion in local money and $9 billion in state funds to be spent on such projects as the intercounty connector, the Montrose Parkway, new buses and bus routes, and a new interchange at Georgia Avenue and Randolph Road.

Initial estimates showed the local portion of the plan could be paid by raising $63 million from a new impact fee charged to developers, $398 million from a 3-cent increase in the county's property tax and $445 million in bonds.