Many Virginia commuters, visions of stop-free driving dancing in their heads, are looking forward to the Dec. 22 opening of Interstate 66 as Liberation Day.

But Virginia highway officials and the National Park Service are worrying over a possible new bottleneck forming at the Potomac River and are busy trying to pass the jam to each other.

The focus of the scuffle is the single-lane ramp that about 1,900 cars now use each hour during the morning rush in order to transfer from inbound George Washington Memorial Parkway to the Theodore Roosevelt Bridge.

In a move that would reroute thousands of cars from Arlington, Fairfax and Montgomery counties, the Virginia Department of Highways and Transportation wants to limit the use of the ramp during these hours to cars carrying four people or more, known in traffic engineers' argot as "high occupancy vehicles," or HOVs.

Unrestricted flow from that ramp, warns Virginia highway planner Richard C. Lockwood, would seriously crowd the bridge and undo some of the benefits of building I-66, the nearly finished, four-lane artery that cuts a 10-mile swath from the Capital Beltway.

But the Park Service replies that limiting exits from the George Washington Parkway, which already is jammed with some 80,000 cars that use it daily, would lead to a hopeless tie-up farther downstream on the parkway as vehicles denied entry to Roosevelt Bridge fought their way onto either the Memorial Bridge or the 14th Street bridge.

The two sides in the dispute appear to be stalemated and it is unclear who will have the final say. The state highways department has submitted a formal request for a permit to put signs on the parkway directing vehicles with less than four people not to use the exit ramp; the Park Service is saying no.

The controversy dates to 1977, when then-U.S. secretary of transportation William T. Coleman approved construction of I-66 inside the Beltway, with certain conditions. One was that it be reserved in peak hours for buses, high occupancy vehicles, emergency vehicles and Dulles International Airport traffic.

State lawyers in Richmond interpret the fine print in Coleman's HOV limitations to include the parkway ramp. Virginia says it is anxious to meet the letter of Coleman's terms, which allowed the state to build the long-delayed highway after years of litigation, acrimony and federal rulings.

Virginia also argues that limiting access makes sense from an engineering view because it would cut traffic on the already heavily congested bridge and encourage car-pooling and use of I-66. Without this limit, Virginia highway officials say, bridge traffic could remain in its current state or grow worse.

About 5,380 vehicles now cross the bridge inbound each hour during the morning rush. Planning estimates show this figure dropping to approximately 4,380 per hour after I-66 opens through from the beltway, provided the Parkway ramp is limited to HOVs. There is no plan to limit access from Rte. 50, the other big artery feeding the bridge, nor to restrict outbound traffic's access to the parkway from the bridge.

Without limits on the inbound parkway ramp, traffic would rise to close to 6,000 cars an hour, according to the estimates. This would cause more jams on the I-66 approach to the bridge.

But attorneys for the Park Service interpret Coleman's terms as exempting the ramp, according to Park Service spokeswoman Sandra Alley. In addition, the Park Service objected on practical terms, she said.

"All other traffic would have to go to Memorial Bridge, which we think would be a bigger problem," Alley said. The ramp to Key Bridge from the parkway has been closed for years.

Jurisdictional responsibility involving the bridge illustrates how bureaucratic conflicts can hinder solutions to traffic problems in the Washington area. The lower 150 feet of the ramp is the responsibility of the Park Service. The rest, as well as I-66 before it reaches the bridge, is owned by Virginia. The District owns the bridge. And the Federal Highway Administration has a say because its funds paid for most of I-66.

D.C. transportation director Tom Downs said that the city does not care who wins the current tussle.

"We are at capacity on the bridge" already, he said.

Downs said that no matter where in Virginia the cars come from, the traffic jams that they create will feed them into the District at about the same rate.

Meanwhile, civic groups that had fought construction of I-66 say they have predicted this problem for years. It makes no sense, they say, to build a high-capacity highway to the Roosevelt Bridge if there are no new bridge lanes to handle the traffic or new roads in the District.

Highway officials respond that car-pooling requirements ultimately could reduce the total number of vehicles coming into the city and ease congestion.

I-66 originally was meant to channel traffic into a network of interstate highways that had been proposed for the District. But most of those roads were canceled in the early 1970s.