Virginia transportation officials dug their shovels into the ground yesterday and started turning dirt on widening a 3.8-mile section of Interstate 66 near Manassas, a project they expect will ease congestion in a spot that backs up at various times virtually every day.

The expansion will add a regular lane and a carpool lane in each direction between the Route 234 Business and Route 234/Prince William Parkway exits. The $37.1 million project is scheduled to be completed by fall 2006, Virginia Department of Transportation officials said.

It will be the first widening to expand the capacity of a major highway in the Virginia suburbs since 2000, when carpool lanes were added to parts of Interstate 95.

"This project is long overdue and will not completely address the congestion problems in that area. However, it's a start," said Board of County Supervisors Chairman Sean T. Connaughton (R), one of several elected officials on hand for the ceremony.

"When this project is complete, it will be coupled with county and other state projects which will make it easier to get into some of the new developments in western Prince William."

The interstate near Manassas is overwhelmed routinely by the tens of thousands of motorists who have moved into western Prince William and points south and west in recent years. The 22-year-old highway serves as their main connector to job centers in the Dulles Corridor, Tysons Corner and Washington. Each day, their homeward commute grinds to a halt at Manassas, where the highway narrows quickly from four lanes to three and then to two.

Some transportation and political officials say part of the road's problem is the design: It is four lanes in Arlington County, bulges to eight through Fairfax County and then shrinks to four lanes again near Manassas. So drivers who generally cruise through the Fairfax portion of the road find themselves in a crawl heading east when they reach Arlington and west at Manassas.

Local, state and federal officials have sought to widen the road inside the Capital Beltway and beyond Manassas for years but have encountered community opposition and a lack of money.

Opposition remains strong in Arlington, where officials have struck a compromise to study adding a third westbound lane to I-66 for about six miles after repeated attempts to add lanes in both directions were rebuffed. Transportation officials hope to finish the study by the beginning of 2005.

The project begun yesterday is a scaled-down version of plans that originally called for a 5.4-mile expansion stretching to the highway's crowded interchange with Route 29.

Those plans are on hold because VDOT doesn't have enough money to complete the full project.

"We're going to move down the highway 3.8 miles until we get funding for the rest of the project, which will move it down to Gainesville," VDOT spokesman Ryan Hall said.

Hall said that funds for the final 1.6 miles won't be available until 2007 and the widening won't be finished until 2010.

VDOT officials have promised that to minimize traffic problems, construction will not be scheduled during rush hour, holidays or when there is an event at the nearby Nissan Pavilion.