Money for adding car pool lanes to Interstate 66 in Fairfax County, which could provide thousands of Washington area commuters with relief from the highway's congestion, was approved by a House subcommittee yesterday.

The House transporation appropriations subcommittee voted to spend $29.7 billion on Department of Transportation and other projects during the federal budget year that starts Oct. 1, including more than $120 million on Metro and road projects in the Washington area.

The subcommittee vote is the first step in the budget process. The bill would need to be approved by the Appropriations Committee, and then by the full House, before being reconciled with a corresponding bill from the Senate.

The subcommittee vote included $8.5 million in federal money for the addition of High Occupancy Vehicle lanes on I-66 between the Capital Beltway and Route 50. The $22.5 million project, scheduled for completion by mid-1992, will draw on another $5.56 million in previously approved federal funds and state contributions, said a spokesman for Rep. Frank R. Wolf (R-Va.).

"Relief is in sight," said Fairfax County Board Chairman Audrey Moore (D), who has made the HOV lanes one of her top priorities. "This is just wonderful news."

I-66 is restricted to HOV traffic during the morning and evening rush hours from the Beltway to Washington, which improves the flow in the heavily used corridor. However, inbound commuters from beyond the Beltway must struggle through heavy traffic to reach that point. The new lanes, which will expand the highway to three lanes in some sections and four lanes in others, will be built on the existing shoulders.

The money for the lanes would be designated a "demonstration project" by Congress, which means the money can be spent without a separate congressional authorization. Virginia officials have complained in the past that demonstration projects reduce the amount of federal transportation money given to the states, and they argued that the state has not received its share in the past.

The panel also approved:

$108 million for Metro construction, including continued work on the Green Line segments scheduled to open in Northwest Washington next spring, Southeast Washington in late 1991 and to Greenbelt in Prince George's County by late 1993.

The subcommittee action assumes the Senate will approve and the president will sign a bill to authorize more than $2 billion in additional Metro construction money. The Bush administration has threatened to veto the new bill.

$9.9 million for improvements to the Baltimore-Washington Parkway.

$1.5 million for programs to promote truck safety.