Gov. Robert F. McDonnell has amended the two-year state budget to prevent money from being sent to the board of the authority that operates Reagan National and Dulles International airports until Virginia’s two new members are seated.

Several legislators and staffers say they believe the change could hold up the state’s $150 million contribution to Metro’s $3 billion planned extension to Dulles Airport, but Metropolitan Washington Airports Authority officials say that McDonnell’s administration has assured them it does not.

McDonnell (R) added the amendment to the existing two-year budget, which ends June 30, but included language about the bond proceeds for the $150 million contribution.

Several legislators said they plan to fight the change Monday when they return to the state Capitol to take up McDonnell’s amendments.

“I think it’s inappropriate for the governor to do that,’’ Sen. Donald McEachin (D-Henrico) said. “That money is needed.”

Transportation Secretary Sean Connaughton and Finance Secretary Ric Brown did not immediately return calls for comment.

The first phase of the $6 billion Silver Line is under construction from Falls Church to Reston and is expected to open in late 2013. Construction on the second part of the project, which will run to Dulles and into Loudoun, is expected to start in January.

McDonnell has resisted giving additional money to the project, and Connaughton has threatened to withhold the $150 million unless some other management changes were made.

Northern Virginia Democrats led an unsuccessful effort in the legislature to secure an additional $300 million for Dulles rail to lower escalating tolls in the region that would pay for the second phase of the Silver Line. The equally divided Senate killed the proposal after McDonnell said he would not spend more than $150 million.

MWAA board members say they believe the language does not affect the $150 million they expect to get from Virginia, and that Connaughton told them there is “no linkage” between seating the new members and getting the money.

Jack Potter, MWAA’s CEO said Thursday that he spoke to Connaughton Wednesday, and he “assured me that this has nothing to do with the $150 million.”

He also said that MWAA and Virginia have “received differing legal opinions about the timing of additional board members.” MWAA, based on an outside legal opinion it received, said it is waiting for the District to pass legislation that would then allow it to amend the compact. Virginia has already passed similar legislation and agreed the appointments would go into effect July 1.

Observers say Virginia’s governor is trying to push through his new appointees on the MWAA board much as he did in getting lawyer Jim Dyke approved to the Metro board of directors sooner than was originally planned.

Potter said the governor’s latest amendment “seeks to accelerate the resolution of that differing opinions in all likelihood through the courts.”

But Virginia legislative committee staff said they believe this change could hold up the $150 million. “That’s my read of it,’’ said Robert Vaughn, staff director of the House Appropriations Committee.

The General Assembly passed a bill earlier this year that would allow McDonnell to seat his appointees but it delayed the seating until July 1. He wants them seated immediately, but the D.C. Council still needs to act — and it has given no indication it plans to do so.

“It sounds like it’s overriding an interstate compact,’’ Sen. Janet Howell said. “If he is, it is truly putting the money in jeopardy.’’

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

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

Earlier this year, McDonnell tried to appease city leaders by quietly informing key leaders on Capitol Hill that he supports budget autonomy for D.C., a major goal for city officials who want to disentangle the District’s annual budgeting process from that of the federal government.

In a letter sent Feb. 9 to House Majority Leader Eric Cantor (R-Va.) and House Oversight and Government Reform Chairman Darrell Issa (R-Calif.), McDonnell said he wanted to give the city the budgetary freedom that “the governors of every state enjoy.” Some observers see the move as an effort to gain the District’s support for extra board members.