Virginia highway officials announced yesterday that they will open a fourth lane on a 6 1/2-mile section of northbound Rte. I-95 between Woodbridge and Springfield next week and make the left lane a high-occupancy vehicle (HOV) lane during morning rush hours.

The new lane and the left-lane restrictions mean that for the first time car pools can travel on a HOV lane from just north of the Fairfax-Prince William county line to the District of Columbia.

The new lane, which will open Thursday barring weather delays, will be created by converting what is currently the righthand shoulder of the highway into an active lane, officials said.

Motorists will be allowed to use the new lane only during morning rush hours, between 6 and 9 a.m. During the same hours, the far left lane will be restricted to vehicles carrying four or more persons.

David Gehr, Northern Virginia district engineer of the Virginia Department of Highways and Transportation, yesterday heralded the shoulder conversion, the first of its kind in Virginia, as an ideal interim solution until a long-planned, multimillion-dollar construction project on I-95, expected to begin in early 1987, is completed. He credited two Prince William County commuters, Carl Peterson and John Powell, with spearheading the project.

In recent years I-95 has suffered daily traffic jams because of the rapid expansion of Fairfax and Prince William counties. I-95 was built to carry a maximum of 6,000 cars per hour, and now routinely carries that many cars and more, Gehr said.

The new lane will start at the Rte. 1 entrance of I-95 and will continue to the Rte. 644 (Franconia Road) exit, just south of the Beltway.

A similar plan for evening rush hours will open for southbound I-95 in early summer, Gehr said. Both interim lanes will be built at a cost of $4.4 million.

Although Gehr predicted the changes probably will be unnoticed except for motorists traveling in the high-occupancy vehicle lane, he said car poolers should be able to shave as much as 15 minutes off their commute. Giving motorists greater incentive to car pool was a major reason for approving the interim lane project, he said.

Gehr did acknowledge, however, potential problems with the plan. Because there will no longer be a right shoulder to the highway, vehicles that break down on the highway could create major disturbances. To prevent this, eight emergency pull-off areas have been built along the 6 1/2-mile stretch.

"We're not kidding ourselves that motorists will break down only in those pull-off areas," Gehr said, but officials hope that drivers who fear trouble will prepare to pull off before their engine fails.

Gehr said that he expects "a transition period" before motorists fully understand the changes, but that the rules for both the temporary lane on the right and the HOV lane on the left will be well marked by signs.

Next week's lane opening will mark a special triumph for Peterson and Powell. The two Prince William residents share rides to Tysons Corner and were the founders of the "Forgotten Commuters."

In 1984, after years of being infuriated by traffic jams on the way to work, the two drafted a plan for a temporary lane and collected signatures on a petition to submit to Gov. Charles S. Robb.

"We kind of looked at each other in the hall and said, 'Let's do something about it,' " Peterson said. "We didn't really complain. We just looked at solutions . . . . We knew there wasn't a lot of money."

To their surprise, state and federal officials were remarkably receptive to the idea, Peterson said. Although the group's plan was not the one adopted, Gehr said the group was "extremely instrumental" in creating the initiative for a plan.

Peterson holds no delusions about the interim plan.

"It's not going to come close to solving the problem, but it's going to be a real improvement," he said. "Anything would be an improvement.

"The traffic on that road is so horrendous you can't believe it."