Gerald Schroeder, a Justice Department lawyer, parked his car yesterday at Metro's newly opened Orange Line station at West Falls Church and rode the subway to work.

"It will probably cost me more than the car pool would," he said. "But if it works out, I'm willing to pay."

Schroeder, a McLean resident, was among thousands of Virginia commuters taking their first rush-hour trips on the 9.1-mile Orange Line extension, which opened Saturday along the median of I-66.

Many passengers expressed delight at bypassing traffic congestion on the interstate and said they were relieved to find parking spaces available at all four new Metro stations. "The lot is less than half full at this point," Schroeder said shortly after 8 a.m. "So far, so good."

The transit authority reported a nearly flawless rush hour for the new stations at East and West Falls Church, Dunn Loring and Vienna. During the first 3 1/2 hours, the authority said, a total of 6,634 passengers boarded trains at the stations, a figure in line with forecasts.

By midday, officials said, the sprawling parking lots at the Vienna station were more than 80 percent full. At the small East Falls Church lot, more than 90 percent of the spaces were taken, they said, and the West Falls Church and Dunn Loring lots were about half filled.

Transit officials had warned that within a few months the lots at East and West Falls Church and Vienna are likely to fill up regularly on weekdays. Spaces are expected to remain available for some time at Dunn Loring, they said. Overall, the new stations have more than 4,000 spaces.

Traffic appeared to flow relatively smoothly on roads leading to the new stations. "We didn't see a significant problem as far as traffic congestion was concerned," said Fairfax County Police Capt. George E. Kranda.

Some drivers, however, ignored traffic restrictions on Haycock Road, a hilly two-lane street leading to the West Falls Church station that has been criticized as hazardous. Three cars could be seen making illegal left turns into the station within 15 minutes. Police said they plan to ticket violators there periodically.

Although ridership counts were not available for the afternoon rush hour, officials estimated that more than 14,000 passengers used the new stations during the day. Officials predicted that daily ridership will climb to 19,000 after the Metrobus system begins service to the new stations June 22. Ridership is expected to exceed 24,000 trips a day by the fall.

Not all passengers got to the new stations by car. Some, such as Laura Oliven, walked to the West Falls Church station. "It's a healthy walk in the morning," she said. Others rode to Vienna on Fairfax City's CUE buses. A few, like Sarah Grusin, arrived by bicycle. "It was great," she said at East Falls Church.

The Orange Line drew some politicking. Shortly after 8 o'clock, Rep. Frank R. Wolf (R-Va.) got on a train at the Vienna station on his way to Capitol Hill. He said he was surprised to find parking still available, adding, "I would have thought by this hour you'd have it filled."

Outside the station, state Del. Stephen E. Gordy handed out political leaflets in his Republican campaign for the Fairfax County Board of Supervisors. At Dunn Loring, an aide to Arlington County Board Member John G. Milliken was pressing Milliken's Democratic drive to oust Wolf.

For some, taking the Orange Line was a spur-of-the-moment maneuver. One woman, who said she was on her way from Charlottesville to Washington, pulled off I-66, parked her car at Vienna and completed her journey by subway. "When I saw the traffic, I figured it couldn't be worse."

For others, the opening of the new stations marked a milestone. "I've been waiting for it for years," said Ted Lopatkiewicz, a federal transportation official who lives near the West Falls Church station. "In fact, it's one of the reasons I moved into this area."