Mame Reiley, one of the most well connected Democratic operatives in Northern Virginia, has decided to step down from the Metropolitan Washington Airports Authority board. (Bill O'Leary/The Washington Post)

Mame Reiley, a longtime member of the airports authority board who chaired the committee that is overseeing the construction of the new Silver Line rail extension to Dulles, resigned this week.

In a Feb. 15 letter to Virginia Gov. Robert F. McDonnell (R), Reiley wrote that “due to a health challenge I currently face, it has become abundantly clear to me that my priorities need to shift so that I may concentrate my time on my health, my family, and my work.”

Reiley has been battling breast cancer since 2010. Her resignation was effective Wednesday. She was one of the longest-serving members of the board of the Metropolitan Washington Airports Authority, which operates Reagan National and Dulles International airports. The authority is also supervising the construction of the 23-mile Metrorail line through Tysons Corner to Loudoun County.

MWAA board member Dennis Martire said the loss of Reiley’s experience will be keenly felt.

“She has shown exceptional leadership on the board, and to lose someone with the institutional knowledge she has is a blow to our board,” he said.

A well-connected Democratic operative in Northern Virginia, Reiley is a major fundraiser with close ties to Sen. Mark Warner (D-Va.) and Rep. James P. Moran (D-Va.)

Warner appointed Reiley to the MWAA board in 2002 when he was Virginia’s governor. She was reappointed in 2008 by Gov. Timothy M. Kaine (D). She served as chairman of the board from 2005 to 2007, during which time the authority made the decision to take over construction of the $6 billion Dulles rail project and management of the Dulles Toll Road to help pay for it. From 2008 until January, Reiley also served as chair of the Dulles rail committee.

Reiley was a fierce advocate last year for placing the proposed Metrorail station at Dulles underground. MWAA’s board approved that location last spring but reversed itself last summer under pressure from regional leaders concerned about spiraling cost estimates for the second phase of the project. Reiley voted for the reversal with the majority, but said, “I believe, to our detriment, we are preparing to act in a shortsighted way.”

In an interview Friday, Reiley affirmed her support for an underground station.

“Even though I’m political and everybody knows that, the decision and vote I took were what I believed was right for the region and right for the authority,” she said.

Tom Davis, an MWAA board member and former Republican congressman, said Reiley was always “a pro” to work with.

“We owe her deep thanks for her leadership,” he said.

Reiley had about two years remaining in her six-year term. McDonnell, who grew up down the street from her near Mount Vernon, will appoint someone to fill her seat.

A McDonnell spokesman said the administration is still awaiting official receipt of Reiley’s resignation and plans an announcement in the coming days.

McDonnell has pushed for increasing the size of the MWAA board to increase the state’s influence, and for naming two new appointees, but the move has been met with resistance from some current members.

Congress passed legislation last year that increased the size of the board from 13 to 17, giving Virginia two additional seats, plus one each for Maryland and the District. Before the bill was passed, Virginia had five representatives, the District and the federal government had three, and Maryland had two.

Staff writer Anita Kumar contributed to this report.