WASHINGTON — The Justice Department proposed a rule on Friday that would expand the definition of a firearm and help close a loophole that has allowed people to buy so-called ghost guns, firearms that are easily assembled from kits but are not regulated by federal gun laws.

The proposal was the latest effort by the Biden administration to crack down on gun deaths. President Biden ordered the Justice Department last month to find a way within 30 days to curb the spread of ghost guns, with an eye toward keeping them from criminals who might not otherwise be able to pass a background check and buy a gun.

“Criminals and others barred from owning a gun should not be able to exploit a loophole to evade background checks and to escape detection by law enforcement,” Attorney General Merrick B. Garland said in a statement announcing the proposal.

“This proposed rule would help keep guns out of the wrong hands and make it easier for law enforcement to trace guns used to commit violent crimes, while protecting the rights of law-abiding Americans,” he said.

After mass shootings this year in the Atlanta area and Boulder, Colo., Mr. Biden issued half a dozen executive actions to address gun violence, including the directive to the Justice Department aimed at stopping the proliferation of ghost guns. Such guns have no serial numbers and are not tracked by the federal government.

“Criminals are buying kits containing nearly all of the components and directions for finishing a firearm within as little as 30 minutes and using these firearms to commit crimes,” the White House said in a statement at the time. “When these firearms turn up at crime scenes, they often cannot be traced by law enforcement due to the lack of a serial number.”

In a budget hearing this week before a House appropriations subcommittee, Mr. Garland told lawmakers that it was unclear whether ghost guns “are defined as firearms themselves.”

Under the proposed rule issued on Friday, gun retailers would need to run background checks before selling kits that contain the parts necessary to make a gun, and gun kit makers would need to include a serial number for certain parts found in firearm kits that are easy to build.

The rule would also require federally licensed firearms dealers to add a serial number to any 3D-printed guns or other nonserialized firearms that they intend to sell.

After the Justice Department issues its proposed rule on ghost guns and publishes it in the Federal Register, the public will have 90 days to suggest changes, the department said in a statement.

The Justice Department said that from 2016 to 2020, law enforcement officers had recovered more than 23,000 firearms without serial numbers from potential crime scenes.

“Although this rule-making will solve only one aspect of the problem, we have an obligation to do our part to keep our families and our neighborhoods safe from gun violence,” Mr. Garland said.

Gun control advocates applauded the move. “Ghost guns undermine nearly every gun law in the country, and they are marketed and sold for that purpose,” Kris Brown, the president of Brady, an advocacy group pushing for gun control, said in a statement. “The rule proposed by the Justice Department today will have a tangible impact.”

Senator Dianne Feinstein, Democrat of California and a staunch advocate of gun control, called the new rule a “common-sense” measure that would cut down on crime and improve public safety.

“For too long, these ghost guns have plagued our streets,” Ms. Feinstein said in a statement. “I’m glad President Biden is fulfilling his promise to ban these guns and will continue to work with his administration to pass common-sense measures to end the gun violence epidemic.”

When Mr. Biden unveiled his executive actions, including the request for a proposed rule about ghost guns, the National Rifle Association vowed to fight the proposals, calling them “extreme gun control actions” that would push states to confiscate more guns.