Metro officials took a group of politicians and government workers for a ride on the Orange Line yesterday to demonstrate that the rail system is prepared to open its nine-mile extension to Vienna on June 7.

"I'm just ecstatic," said Vienna Town Council member Robert W. Robinson after the midafternoon excursion, which included stops at Metro's four new stations. "I was like a little kid today."

The stations, built in the median of Rte. I-66, appeared virtually ready to open. The train traveled smoothly along Metro's new tracks at speeds of up to 75 miles an hour, frequently passing traffic on the highway. Construction crews were completing work on parking lots and access ramps for buses.

More than 12,000 Northern Virginia residents are expected to use the stations at East and West Falls Church, Dunn Loring and Vienna. The parking lots are likely to be jammed, officials said, and nearby streets may become increasingly congested.

Yesterday's outing was largely a political get-together. Metro General Manager Carmen E. Turner chatted with Rep. Frank R. Wolf (R-Va.) and Arlington County Board Member John G. Milliken, who is seeking the Democratic nomination to challenge Wolf.

Falls Church Mayor Carol W. DeLong posed for a photograph at the West Falls Church station. "It's going to be a nice, smooth, fast ride," said Fairfax County Supervisor Joseph Alexander, a member of Metro's policy-setting board.

Carlton R. Sickles, a Metro board member and Democratic congressional contender in Maryland, termed the Orange Line extension a milestone. "It's two-thirds done," he said. When the extension opens, the Metro system will encompass nearly 70 miles. The transit authority's goal is a 103-mile system.