The first phase of the Metro line to Dulles won’t open for two more years, but some watchdogs and board members want calculations of expected costs of operating and maintaining the additional miles of rail and stations.

When Metro’s board of directors approved its $2.5 billion budget this summer, its board said it wanted to develop a multi-year budget for coming years. Part of a multi-year budget would include a more current, clear picture of what the transit agency can expect in running the extension of the rail line to Dulles International Airport and Loudoun County.

“It is certainly a priority for the board” to know the “planning and actions to implement the expansion of the rail and maintaining and operating and funding it,” said Anthony R. Giancola, an alternate federal member of the board.

Another board member — Jeff McKay, who serves as an alternatedirector from Virginia and is a Fairfax County supervisor — said, “We need to be setting aside potential amounts so we don’t have surprises in the future.’’

He said he doesn’t want someone asking for an unexpected couple of million dollars to pay for operations.

“We need to have some numbers that are based in reality that we can work off of,” McKay said.

One of the biggest reasons to know the figures early is that Metro’s funds are already tight.

The transit agency has faced a budget deficit for the past few years, and area jurisdictions have had to pony up funds to fill the gap. Plus, the agency is undertaking a $5 billion capital improvement plan over the next six years for a deteriorating, 35-year-old rail system that hasn’t been properly maintained.

Metrorail oversees 106 miles of track and 86 stations. When its two phases are completed, the Dulles line will add 23 miles to the system. The first part of the Dulles line is under construction and will run from East Falls Church to the eastern edge of Reston. It is expected to be completed in 2013. Details on the funding of the second phase, which will stretch from Wiehle Avenue to Dulles Airport and Ashburn, are being worked out.

The need to figure out how much the Dulles line, commonly called the Silver Line, will cost to operate is imperative, say some board members and outside experts. With the new extension adding about 25 percent more track, some board members expect that it will cost 25 percent more to run.

Knowing the Dulles costs allows the board to “intelligently apply the resources in the right place,” Giancola said. “It is just good, sound strategic budgeting and planning.”

Tom Bulger, a board member who serves as the District’s alternate director, said getting estimates of the cost of operating the first part of the Dulles line is “absolutely critical.”

“We need to know it so Metro can plan accordingly and jurisdictions will have enough time to digest these estimated costs,” he said. “In this economic climate we’re in, dollars are scarce.”

“We are trying to get further out on the budget planning rather than lurching every six months so we can set goals and set performance and do upper-level planning that we need to do,” he added. “You have to have working numbers that have been scrubbed.”

There are no current figures on operational costs for the first phase of the Dulles line, although Metro officials said they are working on them and expect to release them this fall.

The most recent figures of what it will cost to operate part of the Dulles line are from a 2007 Metro plan. It projected that operating and maintaining the first phase of the Dulles line would cost $45.6 million for fiscal 2012, which was then assumed to be the new line’s first year of operation.

That estimate was based on 11 miles of track with five stations. The current first phase is 11.7 miles of track with four new stations in Tysons Corner. The 2007 estimate included salaries, bus fuel, electricity for the train and supplies.

Dan Stessel, Metro’s chief spokesman, said that the agency will “address as part of its multi-year budget process” the expected annual cost to operate and maintain the Dulles line. As part of that review, he said it will also look at how many more employees will be needed.

The operating costs of the line will be “shared by all jurisdictions” and based on a formula the agency uses of a jurisdiction’s ridership, population and number of rail stations, Stessel said. Fairfax and Loudoun counties will pay more than other jurisdictions based on their having more stations and passengers.