The Senate moved a step closer to passing a bipartisan gun safety bill.

WASHINGTON — The Senate on Wednesday moved a step closer to approving bipartisan legislation aimed at keeping guns out of the hands of dangerous people, as a small group of Republicans joined Democrats to break through their party’s blockade and bring what would be the first substantial gun safety measure in decades to the brink of passage.

Fifteen Republicans, including Senator Mitch McConnell of Kentucky, the minority leader, joined Democrats in a crucial test vote that paved the way for the Senate to pass the measure as early as Thursday. The 65-34 vote more than cleared the 60-vote threshold needed to break a Republican filibuster, shattering a three-decade-long string of failures on gun-related legislation. One Republican Senator was absent.

Senator Chuck Schumer of New York, the majority leader, said he intended to bring the bill to the floor for a vote on final passage by the end of the day, though the timing could change.

Speaker Nancy Pelosi of California has said the House would move quickly to clear it once the Senate acts. White House officials said President Biden would sign the measure, calling it “one of the most significant steps Congress has taken to reduce gun violence in decades.”

“This is not a cure-all for all the ways gun violence affects our nation, but it is a long overdue step in the right direction,” said Mr. Schumer. “It’s significant — it’s going to save lives.”

The compromise, the product of an intensive round of talks between a small group of Democrats and Republicans, omits many of the sweeping gun control measures that Democrats and activists have long called for. The negotiations unfolded after a pair of back-to-back mass shootings — one at a grocery store in Buffalo and another at an elementary school in Uvalde, Texas — generated a nationwide outcry for action, and prodded senators in both parties to find at least some common ground after decades of stalemate.

The result is the “Bipartisan Safer Communities Act,” which would enhance background checks for prospective gun buyers under the age of 21, extending the time period from three to 10 days and allowing law enforcement for the first time to examine juvenile and mental health records.

It would also set aside $750 million in federal grant funding to help states implement so-called red flag laws, which allow authorities to temporarily confiscate guns if a court declares a person to be a danger to themselves or others, and for other intervention programs, including mental health courts.

And for the first time, it would include serious current or recent dating partners in a federal law that bars domestic abusers from being able to purchase a firearm, closing what has become known as the boyfriend loophole.

In addition, the measure would toughen criminal penalties for straw purchasing — buying and giving guns to people who are barred from owning a gun — and trafficking guns.

Toiling to keep Republicans on board, Democrats left out their marquee gun control proposals, including a House-passed measure that would prohibit the sale of semiautomatic rifles to people under the age of 21, a ban on the sale of high-capacity magazines and a federal red flag law. They also agreed that the enhanced background checks for younger buyers would expire after a decade, just as the assault weapons ban did in 2004, leaving future Congresses to haggle anew about whether to extend it.

Even so, the National Rifle Association fiercely opposed the bill, saying in a statement that it “does little to truly address violent crime while opening the door to unnecessary burdens on the exercise of Second Amendment freedom by law-abiding gun owners.”

The legislation sets aside millions of dollars, largely in grants, to address mental health in schools and communities, including setting aside $150 million for the national suicide hotline. It also provides funding to boost school safety.

Republican proponents, facing substantial backlash from gun-rights groups and a majority of their colleagues, have been careful to emphasize their success in keeping the scope of the bill narrow, including circulating an endorsement from the National Sheriffs’ Association.

“Sheriffs see, up close, the daily carnage of gun violence carried out by criminals and individuals suffering from mental illness,” the group wrote in a letter. “We appreciate the authors coming together on a bill that can actually save lives, which is written in such a way that allows the states to craft their own unique answers to the questions raised by gun violence.”