More than 100 people debated the merits of adding toll lanes to Interstates 95 and 395 at a public hearing in Woodbridge last night, the public's first opportunity to address the idea.

Two private groups have proposed building high-occupancy toll, or HOT, lanes from the 14th Street bridge to the Fredericksburg area. The plans have won praise from state officials, who are eager to ease the corridor's mounting traffic, but they have drawn considerable opposition from many highway users.

"As much as I'd like to support these proposals, I'm afraid neither is ready for prime time," said David G. Brickley, a former Democratic state legislator from Prince William County.

Brickley said that drivers "shouldn't be penalized again." They shouldn't be "paying for lanes that they've already paid for" through taxes, he said.

Many at the hearing spoke in favor of the proposals, saying they were the only hope to relieve traffic congestion.

"We need more asphalt, and we need more lane miles," said John E. Walvius of Manassas.

The proposals would convert carpool, or high-occupancy vehicle, lanes into HOT lanes, while also widening and extending them.

HOT lanes are free to carpools of three or more, and others pay for the privilege of using them. Tolls rise and fall with traffic, a market manipulation that operators say allows them to virtually guarantee that the lanes won't clog.

Many drivers object to the idea of paying to use the lanes 24 hours a day, seven days a week. As it stands, the lanes are open to all drivers except during weekday rushes, when they are limited to carpoolers. The result, they say, is that even more people will crowd into the regular lanes.

The heaviest opposition has come from slugs, a group of tens of thousands of carpoolers along the I-95 corridor who are afraid that a fee-based highway would end their practice, because drivers might rather pay to use the lanes than pick them up.

Aside from cramping their commuting style, many slugs worry that a reduction in carpooling would further pollute the air.

Carpoolers also are skeptical of promises that they always will be allowed to ride free. Similar promises were made on a toll road in California, where carpoolers now are charged a reduced fee during peak hours.

Last night's hearing came after a briefing on the private proposals. The plans, each of which would cost the companies about $900 million, envision adding a third lane to HOV lanes in the northern parts of the highway; extending those lanes south to the Fredericksburg area; adding commuter parking lots; and augmenting bus service.

A panel of transportation experts is considering the proposals jointly. It will make a recommendation this year on whether the state should proceed with either plan. The commissioner of the Virginia Department of Transportation will make the final decision.

Leaders across the Washington region have embraced HOT lanes as a solution to growing traffic problems and shrinking amounts of money to fix them. Virginia officials are moving forward with plans to build HOT lanes on the Capital Beltway, and Maryland officials are exploring a similar concept on the Beltway, Interstate 270, the Baltimore Beltway and I-95 north of Baltimore.

Public reaction to the concept had been mostly supportive -- until the I-95/395 proposal was put forward.

When Virginia officials announced plans to put HOT lanes on the Beltway, there was barely a blip of opposition. Those could be operational as soon as 2010.

The concept has won support from some environmental groups who normally are loath to back any major highway project.

Environmental Defense gave the Beltway and I-95/395 projects its qualified support yesterday, praising rapid bus service, which is included in the plans. But the organization also warned against allowing the state to use HOT lanes to finance other roads that could induce more suburban sprawl.

"If you do it right, you could generate 23,000 transit users a day," said Michael Replogle, the group's transportation director. "But I'm very concerned . . . that you aren't looking at alternatives as thoroughly as they could be examined."