WASHINGTON — Legislation requested by President Barack Obama authorizing the military to arm and train moderate Syrian rebels fighting Islamic State militants in the Middle East is headed for his signature after a sweeping Senate vote.

The bipartisan 78-22 tally Thursday blended support from Obama’s close Democratic allies and some of his fiercest GOP critics, including top Senate Republican Mitch McConnell of Kentucky. It put leading contenders for the 2016 GOP presidential nomination on opposite sides. Some of Obama’s liberal allies defected.

The legislation also provides funding for the government after the end of the budget year on Sept. 30, eliminating any threat of a shutdown in the run-up to November elections that will seat a new House and decide control of the Senate. The House approved the bill on Wednesday.

Obama said the support from both Republicans and Democrats “shows the world that Americans are united” in combating the Islamic State group. He said the militants thought they could frighten or intimidate Americans, but the Senate vote had showed them they were wrong.

“As Americans, we do not give in to fear,” Obama said. “We pull together. We stand together.”