WASHINGTON – The gun legislation set to hit the Senate floor next month will include universal background checks, Senate Majority Leader Harry Reid, D-Nev., announced Thursday.

Reid had hinted earlier that he might exclude the provision from the bill, as he did with an assault-weapons ban championed by Sen. Dianne Feinstein, D-Calif.

Instead, he introduced a bill that includes background checks, as well as provisions on school safety and gun trafficking.

“In order to be effective, any bill that passes the Senate must include background checks,” he said.

Reid’s announcement came hours after Vice President Joe Biden and New York Mayor Michael Bloomberg teamed up to try to reinvigorate momentum for gun control legislation, urging Congress to be courageous and saying the political risks of supporting such laws were overblown.

Biden and Bloomberg appeared at New York City Hall with families who lost loved ones in the Sandy Hook Elementary School shooting in Newtown, Conn.

“It must be awful being in public office and concluding that even though you might believe you should take action, that you can’t take action because of the political consequence you face,” Biden said.

“The message I want to get across, Mr. Mayor, is that the risk does not exist as is exaggerated today,” because most Americans think the administration’s proposal “is just simple common sense.”

Expanding background checks has been the focal point of President Barack Obama’s gun violence prevention initiative. A number of recent surveys found strong public support for requiring background checks for private sales, including those at gun shows and over the Internet.

But negotiations for a background check measure that would garner sufficient bipartisan support have lagged over disagreements on how sales records on such transfers should be kept.

The Judiciary Committee this month approved an alternative bill by Sen. Charles E. Schumer, D-N.Y., a more sweeping proposal that would be unlikely to attract the 60 votes necessary to prevent a filibuster.

Gun control advocates were alarmed earlier this week when Reid suggested that he would not include background checks in the broader gun legislation if its success on the floor was uncertain.

On Thursday, however, Reid said Schumer’s proposal would be part of the bill, with hopes that a bipartisan compromise could be substituted if a deal is reached.

“I hope negotiations will continue over the upcoming break to reach a bipartisan compromise on background checks, and I am hopeful that they will succeed,” Reid said in a statement. “If a compromise is reached, I am open to including it in the base bill. But I want to be clear: In order to be effective, any bill that passes the Senate must include background checks.”

Reid emphasized that the bans on assault weapons and high-capacity magazines could be offered as amendments to the bill.