The Dulles Corridor Metrorail Project quietly rolled past another deadline this month without any official explanation, the latest in a pattern of delays that has marked the estimated $4 billion rail extension.

Officials planned to complete negotiations by the end of February for the first phase of therail, which would run from West Falls Church to Wiehle Avenue. But the Metropolitan Washington Airports Authority and the commonwealth remain in closed-door talks with two engineering and construction firms — Bechtel and Washington Group International — to take on the project.