A westward-looking view of the Silver Line in Tysons Corner. (Jahi Chikwendiu/The Washington Post)

Officials said Wednesday that completion of the first phase of Metro’s Silver Line could be delayed by at least eight weeks.

“There’s a real question now on when it will be complete,” Jack Potter, the head of the Metropolitan Washington Airports Authority, told members of the MWAA’s Board of Directors at a briefing on the rail project Wednesday.

The MWAA is building the rail line, which will eventually reach Dulles International Airport and go farther into Loudoun County. The announcement means that passenger service on the line is unlikely to begin in December as planned and could jeopardize even a January start.

Metro officials have said that once the MWAA completes work on the project, Metro will need 90 days for testing and training to ensure that the Silver Line is ready for passenger service.

Originally, the MWAA and its contractor, Dulles Transit Partners, said they planned to turn rail-line operations over to Metro in mid-September. An eight-week delay would mean Metro officials must put off their testing.

Metro spokeswoman Caroline Lukas said in an e-mail that it was too early to determine the impact that the delay could have. “There are still a number of variables, so it’s premature to say how this delay will impact the service date,” she said.

If the delay were to push the completion date into November and Metro needed the full 90-day period for testing, the start of passenger service could be pushed back further.

MWAA officials blamed the delay on additional testing that must be done on the rail line’s safety systems.

They referred questions about the tests to Dulles Transit Partners, which declined to comment.

Officials said that the new delays are not related to the automatic train-control system. In June, the head of the Federal Transit Administration raised concerns about unauthorized changes made by the contractor to the control system, one of the key safety mechanisms on the Silver Line and the same system whose failure caused the 2009 Red Line crash that killed nine people.

As a result, additional testing must be done before the rail line is turned over to Metro officials.

Any delay in passenger service could be costly for Metro. Each month passenger service is delayed could cost Metro an estimated $2 million to $3 million in revenue, officials said.

On Wednesday, MWAA officials emphasized that safety trumps any timelines.

“This is about making sure we deliver a safe product,” MWAA board member Earl Adams Jr. said.

The first phase of the Silver Line is made up of five stations and will run from East Falls Church to Wiehle Avenue in Reston. Four of those stations run through Tysons. Last week, contractors received permission to begin construction on the second phase of the project, which will include the stop at Dulles.