Phase one of the Dulles Corridor Metrorail project is six months behind schedule, according to a progress report, but officials supervising the project say they can make up for lost time.

The nearly $7 billion project is now 188 days behind schedule, according to a report by the Fairfax County Office of Financial and Program Audit, shifting the completion date from December 2013 to potentially June 2014.

The two-phase plan will construct the 23-mile Silver Line, an extension of the existing Metro system to Dulles International Airport and Tyson’s Corner in Virginia. The first phase includes building an off-shoot of the Orange Line at East Falls Church to the Wiehle Avenue Station in Reston, Va., while the second portion will add a line reaching Loudon County, Va. and Dulles International Airport.

A spokeswoman for the Dulles Transit Partners, the main contractor for the line, pushed back against the report.

“The project is not behind schedule,” Dulles Transit Partners spokeswoman Leslie Pereira said. “Reports are based on forecasts, projections and possibilities that we are working with airport authorities to mitigate,” Pereira said.

She said the group expects to “put the project back on track” for completion in August 2013 and to be in service by December of that year.

Metropolitan Washington Airports Authority spokesman Robert Yingling also said the line is projected for completion by August 2013 – shortly after the original estimate of July of that year.

“They had to relocate 21 different utilities within the first phase,” Yingling said, explaining that delays resulted from removing wiring and piping from beneath buildings for the rail. “This requires a lot of coordination with the companies that own the lines.”

He added that the first phase of the project is more than 50 percent complete.

Pereira and Yingling both declined to comment on an estimated completion date for phase two, saying plans are not yet finalized. Construction for phase one began in 2009.

The Dulles Airport’s Authority Board of Directors approved an underground stop for the Silver Line Metro in April. The airport is currently inaccessible via Metro.

The project has exhausted a large portion of its more than $300 million contingency fund. Yingling said about $84 million remain.