Del. Lacey E. Putney, I-Bedford, back to camera, chairman of the House Appropriations committee, talks with Sen. Charles J. Colgan, D-Prince William, March 6 during a budget conference committee meeting in Richmond. (Bob Brown/The Associated Press)

State budget negotiators reached a deal Thursday that scuttled $300 million in Metrorail spending and appeared to give Republicans a Democratic defector in the evenly divided Senate.

A majority of House and Senate budget conferees agreed to a two-year, $85 billion spending plan. Republicans need at least one Democrat to vote for the proposal for it to pass the Senate, which has 20 Republicans and 20 Democrats.

Republicans appear to have enlisted Sen. Charles J. Colgan (D-Prince William). He has not signed the tentative deal but has given Republicans a “handshake agreement” that he would do so, said Sen. Emmett W. Hanger (R-Augusta).

“It was a tough call for him,” Hanger said Thursday night.

Colgan’s support suggests that Republicans have the 21 votes needed for passage in the Senate. Passage is not in doubt in the House, where Republicans enjoy a 2-to-1 majority.

Colgan, a social conservative who has voted with Republicans on some issues, could not be reached for comment.

Democratic negotiators held out hope that Colgan and the rest of their party would not approve the plan because it does not include $300 million for the Metrorail line to Dulles International Airport. Even if Colgan signs off on bringing the plan to the Senate floor, “that doesn’t mean he’ll vote for it,” Senate Minority Leader Richard L. Saslaw (D-Fairfax said).

“We have a long way to go,” Saslaw said.

At 85, Colgan is the longest-serving state senator in Virginia history and just last year was persuaded against retirement in order to help Democrats keep control of their slim majority. After the election, the Senate became evenly divided but Republicans took control because Lt. Gov. Bill Bolling (R) breaks tie votes. However, Bolling can’t vote on budget matters.

The budget deal was hatched in the midst of a special session called after Senate Democrats blocked passage during the regular session in a dispute over spending and committee assignments.

After Democrats agreed to divorce their demand for more committee power from the budget process, the Senate signed off on a spending plan that added millions of dollars for schools, safety-net programs and transportation.

Although Senate Republicans made peace with that deal, it was a tougher sell in negotiations with the more conservative House.

The Senate version prevailed in some areas, including the cost-of-competing funds, which are usually provided to Northern Virginia schools to help them attract staff in that expensive job market.

The budget proposed by Gov. Robert F. McDonnell (R) included the funds for teachers but cut the $65 million usually provided for support staff. The budget plan passed by the Senate restored $60 million of that, and the House proposal included $24 million.

Negotiators have agreed to include $40 million in the budget for cost-of-competing, with $28 million of that devoted to the first year, said Sen. Walter A. Stosch (R-Henrico), chairman of his chamber’s Finance Committee. Legislators could come back in the second year of the budget to request more funds, he said.

The Senate budget also had included an estimated $125 million for toll relief in Hampton Roads. That was cut during the negotiations, but with a promise from the administration that it will find another way to provide toll relief.

Budget conferees also have agreed to direct state auditors to study how cost-of-competing payments are calculated and what school districts should receive the funds, Stosch said. The funds are distributed across an area stretching from Culpeper to the Washington suburbs.

Transportation Secretary Sean T. Connaughton visited with negotiators earlier Thursday and said McDonnell would not agree to the additional money for rail to Dulles.

Legislators do not plan to return for further negotiations but the budget bill will be voted on April 17, Saslaw said.

Earlier this week, House and Senate budget conferees had reported progress on most areas of the spending plan, with the exception of transportation. Negotiators also said they were close to working out their differences related to higher education.