Virginia and District officials have called for changes in a congressionally mandated plan to ease car pool restrictions on Shirley Highway, warning that the proposed rules may increase congestion on the heavily traveled highway.

Under legislation enacted last year, car pool regulations on the highway's express lanes are to be relaxed in a one-year experiment, probably starting in January.

The express lanes are to be opened to all vehicles, except during rush hours when the lanes would be restricted to four-member car pools.

The Northern Virginia Transportation Commission, a panel representing county and city governments, recently joined other Virginia and D.C. agencies in objecting to the plan.

The commission said the move "would choke the express facilities without relieving congestion on the conventional lanes." Buses also "would be penalized by traffic slowdowns" on the reversible express lanes, the group said.

The commission's resolution, adopted unanimously earlier this month, followed similar recommendations last summer by the Virginia Department of Highways and Transportation, the D.C. Department of Public Works, and the Shirley Highway/I-66 Steering Committee, a special panel set up by the Metropolitan Washington Council of Governments.

Federal Highway Administration officials said the issue is under review and no decision is expected for some time.

A spokesman for Rep. Stan Parris (R-Va.), who proposed the relaxed car pool rules, said that Parris opposes any immediate shift in the plan but would consider revisions if traffic tie-ups occur.

"Give it a chance. If it doesn't work, then we'll try something else," said Sydney E. Courson, Parris' press secretary. "The congressman believes that the express lanes are underutilized -- that they're sitting there 18 hours a day with, in essence, nobody on them."

Under Parris' plan, the express lanes would be limited to four-member car pools from 6 a.m. to 9 a.m. and from 3:30 p.m. to 6 p.m. The express lanes currently are restricted to car pools, buses and emergency vehicles at all hours.

The Northern Virginia commission recommended that each of the restricted periods be extended 30 minutes in an attempt to avoid back-ups similar to those that have occurred on I-66, where car pool limits were eased earlier this year.

Under the commission's proposal, four-member pools would be required from 6 a.m. to 9:30 a.m. and from 3:30 p.m. to 6:30 p.m. Similar recommendations also were made by the District, the Virginia highway agency and the steering panel.

In addition, the Virginia and District agencies urged that the express lanes be restricted to two-member car pools and motorcycles at all times other than rush hours.

Some Virginia and District officials have disputed Parris' contention that the express lanes are underused and have argued that relaxing the restrictions may discourage car pooling.

In addition, officials contended it may later prove difficult to tighten car pool requirements even if problems occur during the one-year test.

"It's always tough to take something back once it's been given. We've seen that on I-66," said Richard K. Taube, the Northern Virginia commission's executive director.

The relaxed car pool rules are scheduled to go into effect after the District completes a $5.9 million overhaul of the southbound (George Mason) span of the 14th Street bridge. The renovation work is expected to be finished by late November or December.

Parris recently opposed a congressional move to give the District and Virginia more control over the Shirley Highway test.

Courson said Parris wanted federal officials to oversee the experiment because he feared that state and city officials would not allow "a full and fair test" of the relaxed rules -- a point disputed by some officials.

That controversy ended last week when Congress shelved a massive highway bill. The amendment opposed by Parris had been attached to the $7.2 billion highway measure.