One of Northern Virginia’s four representatives to Metro’s board of directors may soon have to step down — or move to a less powerful position — so a state appointee can take a spot overseeing the $2.5 billion transit authority.

Virginia lawmakers passed legislation in the spring allowing Gov. Robert F. McDonnell (R) to appoint a person to serve in one of the 16 seats on Metro’s board.

How the changes will unfold isn’t clear. One possibility: Northern Virginia’s local jurisdictions would lose one of the eight coveted voting slots.

“The governor could wait until a term is up, but he seems intent on taking responsibility now, and therefore someone will need to step aside or be replaced,” said Jim Dinegar, president and chief executive of the Greater Washington Board of Trade, whose group has studied Metro’s governance.

McDonnell isn’t providing details, but Courtney Ware, a manager of policy and communication for the Virginia Department of Rail and Public Transportation, wrote in an e-mail that the governor is “still considering candidates, and a formal announcement will be made when a decision is made.”

McDonnell has long pushed for the power to appoint a member to Metro’s board. Last year, he threatened to withhold funds for capital improvements unless he received the authority.

“The state is the largest single contributor of public funds to Metro from our side of the Potomac,” said Virginia Secretary of Transportation Sean Connaughton. “It has grown over time, the amount of money we’ve put in. We’re actively involved in the new Metro capitalization program, the Dulles rail project and increased safety oversight of Metro. The system is facing a lot of challenges, and the state has a vested interest in being at the table.”

But Northern Virginia’s representatives on the Metro board are reluctant to give up their seats. The local jurisdictions say they contribute more money to Metro than the state.

“Arlington will never step away from Metro,” said Mary Hynes, a principal director on the Metro board and vice chairwoman of the Arlington County Board. “We’ve been in this game for 35 years, building the system, and we’re committed to the system.”

Metro’s board of directors has come under scrutiny since the 2009 Red Line crash that killed nine people and injured dozens. Outside groups, including the Metropolitan Washington Council of Governments, the Board of Trade, and the Government Accountability Office, have said the board needs to more clearly define its oversight role.

In November, a task force of the Board of Trade and the Council of Governments recommended that Metro change its governing compact to eliminate nonvoting alternates and increase the number of voting members in each jurisdiction from two to three, with at least one member appointed by the chief executive of each jurisdiction.

Under the current procedures, Virginia, Maryland, the District and the federal government each appoint two voting principal directors and two nonvoting alternates. The alternates vote in committee meetings but can only vote in full board meetings in the absence of the voting member, according to Metro’s board procedures. Fourteen of the seats on the Metro board are filled — nine by relatively new members.

Each jurisdiction appoints its representatives differently.

The federal representatives are appointed by the General Services Administration.

In the District, the D.C. Council appoints two of the Metro representatives — one of the voting and one of the nonvoting members. The mayor’s office traditionally appoints the other two.

Maryland selects its representatives from Washington Suburban Transit Commission members, who are chosen by the governor and Prince George’s and Montgomery counties. The governor’s appointees serve as the voting principal directors on Metro’s board; the counties’ appointees serve as alternates.

In Virginia, the Northern Virginia Transportation Commission (NVTC) appoints two elected officials to Metro’s board. They traditionally have served as voting members. One usually comes from Fairfax County, and the other from Arlington County. The alternates typically are appointed by Fairfax and from the City of Alexandria.

The new Virginia amendment requires the NVTC to give the governor one of its two voting seats.

“The two governors and the mayor of D.C. need to exercise their responsibility and hold the board accountable in the oversight of Metro’s operations,” Dinegar said. “That’s a whole lot easier to do if you’re responsible for appointing at least one of the board members.”