Metro may have to spend millions more than anticipated to operate the new Silver Line because trains will have to travel farther east than planned, according to two people with knowledge of the problem.

Transit officials originally expected eastbound Silver Line service to end at the Stadium-Armory stop, according to the two sources. But officials have since concluded that the tight turning space near the station would make it difficult for trains to reverse course there. Instead, trains will travel five additional stops to Largo before turning around to head back toward Virginia.

The change could cost Metro $4.5 million a year more to operate the line, according to the two people familiar with the problem and the plan to deal with it. The individuals spoke on condition of anonymity because they are not authorized to speak publicly on the issue.

Officials are expected to detail the plan to the Metro Board’s Customer Service and Operations Committee next week as part of a larger presentation on Silver Line service.

The extended distance will require 20 to 30 more rail cars, which can be pulled from existing stock but will require Metro to ramp up maintenance on the existing fleet to ensure they are ready, sources said. The plan will also require additional personnel.

Metro spokesman Dan Stessel said he could not comment because the board has not been briefed on the issue.

The first phase of the $5.6 billion Silver Line rail extension, which will run from East Falls Church to Wiehle Avenue in Reston, is expected to be completed in August 2013. Once construction is complete, Metro officials said it could take six months for service to begin.

The Metropolitan Washington Airports Authority is overseeing construction, but the Washington Metropolitan Area Transit Authority will be responsible for operating the rail line. Airports authority officials expect to award a contract next year to begin construction of Phase 2 of the line, which will extend to Dulles International Airport and into Loudoun County.

Tom Downs, chairman of the Customer Service and Operations Committee, said Metro General Manager Richard Sarles recently told board members there were some potential problems with the “turn back” at the Stadium-Armory station. The physical configuration of the tracks there would make them difficult to retrofit to become an active turnaround, Downs said. But Downs said the general manager did not offer any other details, including what it might cost to retrofit the area or what it might cost to extend service to Largo.

In October 2011, Carol Kissal, Metro’s chief financial officer, told the Metro board’s finance committee that servicing the 11.5 miles of rail and five stations now under construction in Virginia is expected to cost $20 million in fiscal 2013. That expense includes equipment to run the railroad, plus recruiting and training train operators, station managers, escalator and rail car maintenance personnel and police officers. It is expected to cost $45 million in fiscal 2014 and $44 million in 2015.

According to estimates released in October, Metro officials think Silver Line ridership will top 14 million in its first full year of operation. They estimated that total additional passenger fare revenue from the Silver Line will be about $2.8 million per month — a figure that includes both new and existing passengers. Northern Virginia officials believe the rail line will spur economic development along the corridor and provide a critical transportation alternative for commuters and travelers.