The track is laid, the platforms are finished and brand-new parking meters--still wearing protective plastic--are installed in some station lots. After more than 20 years of planning, the last leg of Metro's 103-mile subway system--6.5 miles of the Green Line from the District into Prince George's County--is nearly complete.

Some transit sources say progress has been so swift, they are now expecting to beat the March 2001 opening date and could launch service as early as January 2001, in time for Inauguration Day.

"We are going to be under budget and, perhaps, ahead of schedule," said Takis Salpeas, assistant general manager at Metro.

Construction on the $1 billion project is almost finished. Now the focus shifts to 12 months of testing--making sure tracks, trains and operating systems work--and the wait for 110 rail cars being built to provide the new service. A few weeks ago, Metro officials threw the switch that sent 750 volts of power to about two-thirds of the rail; the remaining track will get power by mid-January.

The last segment of the Green Line will link the Anacostia station in the District to the Branch Avenue station in Prince George's County. It runs along a southeast route that stops at Congress Heights in the District before crossing into Prince George's, with stations at Southern Avenue, Naylor Road, Suitland and Branch Avenue. At the Branch Avenue terminus, Metro is also building a 37-acre rail yard with the capacity to store 116 cars.

The five new Green Line stations, which were put on hold for most of the 1980s because of local disputes over the route, are the last to be finished under Metro's original plan for a 103-mile rail system.

But Metro General Manager Richard A. White says Branch Avenue is hardly the end of the line for the transit agency.

"There's a higher level of receptivity to transit extensions in the region than there was even four years ago," White said, adding that Metro is considering building transit to Largo and Tysons Corner as well as Dulles International Airport. "This can be either the end of a chapter or the end of a book. We think it's the end of a chapter."

For Southeast Washington and Prince George's County, the new service will bring rapid transit to a region that is heavily reliant on public transportation but has had to make do with buses that wind their way along crowded roads.

"In those communities, it's going to be very comforting to be finally served by rail," White said.

Metro officials expect that 50,000 passengers a day will be riding the new service by the end of its first year of operation.

John P. Davey, who represents Prince George's County on the Metro board of directors, said the Branch Avenue extension will also offer commuters from fast-growing Southern Maryland an alternative to traffic-choked highways to the District.

"It gives the whole southern section of our jurisdiction an opportunity to get out of their cars and not fight their way up Route 4 or Route 5 every morning," Davey said. All four stations in Prince George's County have parking, ranging from 370 spaces at Naylor Road to 3,100 spaces at Branch Avenue.

Completion of the Green Line to Branch Avenue also allows transportation planners to think about a transit link from Prince George's across a new, expanded Woodrow Wilson Bridge to Alexandria, Davey said.

"Branch Avenue gives us the opportunity to think about how we can connect Northern Virginia with Southern Maryland by transit, how we can move people, goods and services across the Potomac," he said.

Since construction on the Branch Avenue extension began in 1995, Metro has faced a number of challenges along the route. Residents near St. Elizabeths Hospital, backed by the Sierra Club, protested that running surface rail across hospital property that had been the site of an incinerator ash dump would present environmental hazards. Metro opted to tunnel under the area, according to Sabit Ghosh, project manager.

The alignment also ran through National Park Service land along Suitland Parkway, where dozens of trees were lost. Federal and state officials later demanded that Metro buy and plant new trees elsewhere on the land to replace those displaced by the rail line.

CAPTION: Electrician Stanley Lee works on the Green Line tunnel under Congress Heights station. Transit officials say they could begin service as early as January 2001.