Gov. Robert F. McDonnell will announce Friday afternoon that he is appointing James Dyke to the Metro Board of Directors as he looks to exert some long-sought authority over the second-busiest subway system in the nation, administration officials confirmed Friday.

His decision to appoint Dyke fulfills a promise to appoint a Northern Virginian to the 16-member Washington Metropolitan Area Transit Authority board that he has insisted for more than a year needs more input and oversight from state government.

The change will force the Northern Virginia Transportation Commission, comprised of 19 local and state elected officials plus the state’s public transportation director, to give the state one of its seats.

“Somebody would have to step off as a voting member because [the governor] clearly wants to appoint someone who would have a vote to WMATA,” said Mort Downey, a federal principal member of Metro’s board.

Dyke, a partner at McGuire Woods, will serve on both the NVTC and Metro boards. He has worked for Democrats, former Gov. Doug Wilder and Vice President Walter Mondale, and is active in the Northern Virginia business community. He was chairman of the Greater Washington Board of Trade last November when it called for dramatic changes to Metro.

The joint task force of the Greater Washington Board of Trade and Metropolitan Washington Council of Governments recommended that Virginia, Maryland and the District change the agreement that governs Metro to increase the number of principal members from each jurisdiction from two to three, with one member appointed by the chief executive of each jurisdiction.

Each jurisdiction, plus the federal government, currently appoints two principal and two alternate directors. Both Maryland Gov. Martin O’Malley (D) and D.C. Mayor Vincent C. Gray (D) have backed McDonnell’s effort.

The task force criticized Metro’s structure as outdated. In the wake of that report — and another from the Metro Riders’ Advisory Council — the transit authority has been reexamining and redefining how it operates.

McDonnell (R) had pushed for months for at least one seat on the board but had been thwarted repeatedly by local officials in Northern Virginia, primarily Democrats, who opposed the effort.

In April, Virginia’s divided General Assembly unexpectedly voted for a budget amendment giving the governor a seat starting July 1.

Downey said the Metro board has not discussed who would be the person to step down as a result of McDonnell’s appointment.

This year the board has undergone significant turnover, with more than half of the 16-member board being replaced as Metro tries to move beyond the shadow of recent financial and safety troubles.