A Senate bill extending health and other benefits to the same-sex domestic partners of gay and lesbian federal employees would cost the government $704 million over its first decade, the Congressional Budget Office said.

In a May 11 cost estimate, CBO said that S 1102, the Domestic Partnership Benefits and Obligations Act sponsored by Sen. Joseph Lieberman, I-Conn., would by 2020 increase mandatory spending by $310 million and discretionary spending by $394 million. Increased health coverage through the Federal Employees Health Benefits Program would account for $649 million of the total cost increases.

But the Senate's bill is not as expansive as the House's version, HR 2517. Unlike the Senate's bill, the House version would also extend benefits to domestic partners of federal retirees. CBO last December found the House version would cost $898 million in its first decade.

CBO estimated that 0.33 percent of the 2.7 million federal and U.S. Postal Service employees — or about 8,900 people — would register their same-sex domestic partnerships. About 4,000 federal employees and about 2,000 U.S. Postal Service employees would likely switch from self-only health plans to family coverage, CBO said.