WASHINGTON — The Senate on Thursday completed a five-year, half-trillion-dollar farm bill that cuts farm subsidies and land conservation spending by about $2 billion a year but largely protects sugar growers and some 46 million food stamp beneficiaries.

The 64-35 vote for passage defied the political odds. Many inside and outside of Congress had predicted that legislation this expensive and would have little chance of advancing in an election year.

Senate Republican leader Mitch McConnell called it “one of the finest moments in the Senate in recent times in terms of how you pass a bill.”

The bipartisanship seen in the Senate may be less evident in the House, where conservatives are certain to resist the bill’s costs, particularly for food stamps.

Food stamp spending has doubled in the past five years, and beneficiaries have grown from by about 20 million to 46 million. The program’s budget is now about $80 billion a year, comprising 80 percent of the spending in the farm bill.

While overall spending under the bill has climbed because more people are receiving food stamps, the committee head, Sen. Debbie Stabenow, D-Mich., and the top Republican, Sen. Pat Roberts of Kansas, said the bill would save $23 billion over the next 10 years compared with spending under the current farm bill.