New financial projections show that Metro's Silver Line to Washington Dulles International Airport may end up a month behind schedule and, when complete, will have 100,000 fewer riders than Metro predicted a year ago.

Metro's forecast, released Tuesday, shows that a monthlong delay in the opening of the first segment of the rail line -- originally scheduled for late 2013 -- could cost the transit agency between $2 million and $3 million in lost revenue.

But an agency spokesman said Metro is just trying to account for all possibilities in drafting its budget and that the agency's board will look at a range of hypothetical opening dates as it calculates operating costs for the Silver Line.

The Metropolitan Washington Airports Authority, which is building the $6 billion line and will eventually turn it over to Metro to operate, said there's no indication that the project is behind schedule.

"At this point in time, we're on schedule," said project director Patrick Nowakowski. "I have no knowledge of what [Metro has] done. I don't know what their assumption is in their budget."

The authority said last year that the rail line was as much as six months behind schedule, but the authority has since been told that the contractor's efforts to make up that time succeeded.

Metro's new projections also show it will have 100,000 fewer riders than it projected last year, and about a million fewer riders than it predicted in 2004, though it still expects Silver Line ridership to top 14 million in its first full year of operation.

Metro's pessimistic calculations came the same day Virginia Gov. Bob McDonnell wrote to compliment the airports authority, with which he has been feuding for months. McDonnell praised the authority for trimming the cost of the rail line's second phase and for instituting ethics reforms to ensure the integrity of the board.

"It is my hope that we are at a turning point in the history of MWAA," McDonnell wrote.