WASHINGTON (Reuters) – By one vote, Senate Republicans on Thursday blocked a bill to shave billions of dollars from health plans that contract with the federal Medicare program and avert a pay cut for doctors.

On a 59-40 count, mostly Democratic backers fell shy of the 60 needed to clear a procedural roadblock and move towards final congressional passage of the measure earlier approved by the House of Representatives.

Senate Democratic Leader Harry Reid switched his vote from “yea” to “nay” to allow him to bring the measure up again at a later point. So the final tally was 58-40.

Blocking the bill, with about $13 billion in cuts to private health insurers in Medicare, paves the way for making a compromise with less harsh cuts likely to emerge.

In its current form, the legislation would shave reimbursement for health insurers such as Aetna Inc, Humana Inc and UnitedHealth Group Inc, which contract with the government to sell insurance to seniors.

Senators had abandoned efforts at a compromise with less-harsh cuts, lawmakers said.

Presidential candidate Barack Obama interrupted his campaign to return to Capitol Hill and vote with fellow Senate Democrats.

The legislation won unexpected overwhelming support in the House earlier this week. That boosted chances, once seen as slim, that it could garner enough votes to sustain a promised presidential veto.

U.S. lawmakers face a June 30 deadline to pass legislation blocking a scheduled 11 percent pay cut for doctors who accept Medicare patients — considered a highly unlikely outcome in an election year. Cuts to the private plans would help keep doctors’ payments intact.

Oxygen providers such as Apria Healthcare Group Inc and Lincare Holdings Inc back the bill, because it proposes less harsh cuts than a prior Senate version, according to an industry group.

Pharmacy benefit providers such as Medco Health and Express Scripts oppose the bill because it requires pharmacy companies to pay pharmacies within 14 days, rather than a standard 30-day cycle.

(Reporting by Tom Ferraro and Kim Dixon; Editing by Braden Reddall)