The House of Delegates killed a bill Thursday that would have allowed Gov. Robert F. McDonnell to seat two new appointees to the board of the authority that operates Reagan National and Dulles International airports after Democrats refused to allow it take effect immediately.

But Del. Joe T. May (R-Loudoun), chairman of the Transportation Committee, who filed the bill, said the issue is not dead. A similar Senate bill will be considered.

Earlier this week, the House passed the bill allowing the Republican governor’s two appointees to be seated on the authority managing construction of the $6 billion Metrorail expansion to Loudoun County but not until July 1. After it was amended, the bill died.

In November, McDonnell tapped Todd Stottlemyer of Oakton, chief executive of the Fairfax-based technology firm Acentia, and businesswoman Caren Merrick of McLean, an unsuccessful candidate for state Senate last year, to join the board of the Metropolitan Washington Airports Authority.

“Today, House Democrats voted to block enactment of emergency legislation that would have increased Virginia representation on the MWAA board, a body charged with overseeing the two largest airports in Virginia, the Dulles Access Road, the Dulles Toll Road and the Dulles Metrorail Extension project,’’ McDonnell said in a statement.

“The move today is contrary to federal law and delays the seating of our new representatives during a time when important project decisions are pending before MWAA,” the statement said. “The decision to block the emergency clause in this legislation does not represent the best interests of the citizens, businesses, taxpayers and toll payers of Northern Virginia or the commonwealth.’’

Democrats, who hold 32 of the House’s 100 seats, balked at passing the bill with a provision that would have allowed it to be signed into law immediately.

In a statement, House Democrats said they support the Metro project and adding more Virginia voices to the board but they opposed the process.

“The case has not been made that this legislation is an emergency, and there is no reason that HB 252 cannot be passed in the normal course of General Assembly business,’’ the caucus said. “In rushing the committee process to get HB252 passed without the testimony of the involved parties, insufficient time was spent considering the impact of our decision upon Virginia taxpayers.”

Transportation Secretary Sean Connaughton wrote a letter to House Minority Leader David Toscano (D-Charlottesville) urging him to support the bill.

“As has been demonstrated in blood, sweat and tears over the past year, the McDonnell administration is committed to completing the Dulles Metrorail Extension,’’ he wrote. “We respectfully request you and your colleagues demonstrate the same commitment by supporting passage of HB 252 with its emergency clause.”

Three Democrats voted with Republicans -- two conservative Democrats as well as Del. Ken Plum (Fairfax). Plum said it is “past time for reform” on MWAA.

The MWAA has been criticized for a lack of transparency in its operations and for its management of the 23-mile Dulles rail project. Phase 1, which is under construction from Falls Church to Reston, could run as much as $150 million over budget. The inspector general for the federal Transportation Department is conducting an audit of MWAA. It is expected to be completed in the spring.

The new appointments come out of legislation introduced by Rep. Frank R. Wolf (R-Va.) to expand the board from 13 to 17 members. The bill called for Virginia to get two new appointments, while Maryland and the District were each to get one more. Before the bill was passed, Virginia had five representatives, the District and the federal government each had three, and Maryland had two.

McDonnell has long sought more seats on the MWAA board and other regional transportation organizations. He pushed to have a representative on the Metro board and eventually persuaded the General Assembly to give him the authority to make an appointment.

Wolf’s legislation also prohibits board members from serving past the end of their terms. Members also could be “removed for cause” by the governors of Maryland and Virginia and the D.C. mayor. The executive branch of the federal government already had that authority.

The airports board voted in September to authorize then-Chairman Charles Snelling to publicly oppose Wolf’s efforts.

A spokeswoman for the board said the members would not comment on the appointments bill until the legislation is signed.