WASHINGTON (Reuters) -A stopgap spending bill that would avert an Oct. 1 government shutdown fell short in the U.S. Senate on Friday, as Democrats withheld support for the legislation while demanding higher spending for healthcare.

The 44-48 vote, coming on the eve of a week-long congressional recess, raises the chances that federal agencies will shut down if a deal between Republicans and Democrats cannot be struck before current funding expires at midnight on Sept. 30.

Only one Democrat voted for the bill, leaving it short of the 60 votes needed to advance under Senate rules.

It was unclear whether Senate Majority Leader John Thune would call the Senate back from its break to try again next week.

Congress has struggled to pass spending legislation in recent years due to rising partisan tensions, repeatedly raising the threat of a shutdown that would leave government workers unpaid and a wide range of services disrupted.

The rejected bill, which passed the Republican-controlled House of Representatives earlier in the day, would keep federal agencies operating at current funding levels through November 21, while providing $88 million to protect members of Congress, the executive branch and the Supreme Court from the threat of political violence in the aftermath of conservative activist Charlie Kirk's assassination.

Democrats had demanded additional funding for healthcare tax credits under the Affordable Care Act and the restoration of funding cut from the Medicaid healthcare program for lower-income Americans. But that effort failed 47-45 in an earlier floor vote.

The annual funding debate covers only about one-quarter of the federal government's $7 trillion budget, which also includes mandatory programs such as Social Security and Medicare, as well as payments on the nation's $37.5 trillion debt.