Secretary of Transportation Elizabeth Hanford Dole has cleared the way for Virginia officials to expand the hours during which controversial car pool restrictions are imposed on Rte. I-66 inside the Capital Beltway.

At the same time, Dole said in a letter released yesterday, state officials may need to further weigh their proposals to change the car pool rules because of the Metro subway system's plan to open an Orange Line extension to Vienna on June 7. The rail extension has been built in the I-66 median.

"I am sure Virginia would want to evaluate the impact of a major change in transportation services, such as this, before the hours of operation [on I-66] are modified," Dole said in a letter made public by Rep. Frank R. Wolf (R-Va.), an advocate of relaxing the I-66 car pool regulations.

Wolf, who won congressional approval of a 1983 measure that eased the car pool rules, hailed Dole's statements as an endorsement of his proposal last December to delay any further change in the car pool regulations for a year. Wolf urged the delay to study the impact of the planned Metro extension.

Dole's actions represented a key development in one of the Washington area's most tangled highway issues. Under the legislation backed by Wolf, the rush-hour restrictions were relaxed to permit use of the road by car pools consisting of three persons rather than four.

In addition, the rush-hour periods during which the rules are in effect were shortened. The car pool requirements are imposed on eastbound traffic from 7 to 9 a.m. and on westbound traffic from 4 to 6 p.m.

In a recent report to Congress, Dole said she has ruled that the three-person requirement should remain in effect until congestion becomes severe, probably in the early 1990s. This plan had previously gained widespread support from transportation and other officials in the Washington area.

Virginia and other local officials have urged, however, that the rush-hour periods be expanded, triggering objections from Wolf. Under the proposals, the restrictions would be in effect from 6:30 to 9 a.m. and from either 3:30 or 4 p.m. to 6:30 p.m.

Dole said that this issue "should remain the prerogative" of Virginia officials. "State decision-makers should have the flexibility to respond as local transportation needs change," she said. The Virginia Highway and Transportation Commission is expected to consider the issue soon.

In a related development yesterday, the Metro board approved changes in more than 60 bus routes in Northern Virginia areas that will be served by the planned Orange Line extension. The shifts, scheduled to take effect June 22, are designed to cut costs and improve service to the new rail stations.

Bus service will be expanded in areas including Centreville, Franklin Farm, Chantilly and Fairview Park, along with sections of Vienna and Reston. Most express bus service on I-66 will be halted as a cost-cutting move, and passengers will have to transfer to the new rail stations.

The changes will affect many routes on 12 major Metrobus lines. These lines are designated as 1, 2, 3, 4, 5, 10, 22, 23, 24, 26, 28 and 38. The 29Z route will be revised and the 66X route will be eliminated.

Some of the Metro system's initial proposals for altering these routes were modified as a result of protests by bus riders at hearings in January. In one key change, officials said, the transit agency agreed to retain bus service between Reston and the Pentagon and Crystal City.

Riders are expected to gain quicker trips, but pay higher fares. The shifts are designed to save Metro nearly $900,000 a year.