WASHINGTON — President Biden, calling gun violence in the United States “an international embarrassment,” took a set of initial steps on Thursday to address the problem, starting with a crackdown on the proliferation of so-called ghost guns, or firearms assembled from kits.

Acknowledging that more aggressive actions like banning assault weapons, closing background check loopholes and stripping gun manufacturers of their immunity from liability lawsuits would have to wait for action from Congress, he said it was nonetheless vital to do what he could on his own to confront what he called an epidemic of shootings that are killing roughly 100 Americans a day.

“We’ve got a long way to go — it seems like we always have a long way to go,” Mr. Biden said during an appearance in the Rose Garden, weeks after two mass shootings, in Georgia and Colorado, left 18 people dead and put the administration under intense pressure from the left to take action.

While the moves the president announced fall far short of the broad legislative changes long sought by proponents of making it harder to buy guns, especially semiautomatic weapons often used in mass shootings, they addressed narrower issues also of intense concern to many Democrats and supporters of gun regulations.

The most substantive of the steps was directing the Justice Department to curb the spread of ghost guns. Kits for these guns can be bought without background checks and allow a gun to be assembled from pieces with no serial numbers.

Mr. Biden said he wanted the department to issue a regulation within a month to require that the components in the kits have serial numbers that would allow them to be traced and that the weapons be legally classified as firearms, with the buyers subjected to background checks.

“I want to see these kits treated as firearms under the Gun Control Act,” the president said.

The Bureau of Alcohol, Tobacco, Firearms and Explosives estimated that 10,000 ghost guns were recovered by law enforcement in 2019. Cities like Philadelphia, Baltimore and San Diego have seen significant increases in the number of such guns recovered each year since then.

Ghost guns, experts said, have become particularly appealing to criminal organizations and right-wing extremists who want access to untraceable firearms that do not require any background checks. They are often linked to shootings in states like California that have instituted strict gun laws.

The focus on ghost guns also underscored the White House’s intent to address gun violence broadly and not just the mass shootings that get widespread news coverage.

“Ghost guns are disproportionately impacting gun violence in communities of color and undermining states with strong gun laws,” said Christian Heyne, the vice president of policy at Brady: United Against Gun Violence, a prominent proponent of tighter gun laws.

Ghost guns have also been used in some mass shootings, including one in 2013 at Santa Monica College, in California, in which five people were killed; one in 2017 in Northern California, in which a gunman killed his wife and four others; and one in 2019 at a California high school, in which a 16-year-old killed two students and injured three others.

Even a modest step like addressing the issue of ghost guns, which have been in circulation for years, shows how paralyzed the politics surrounding gun control have become.

Despite the National Rifle Association’s financial troubles, the group’s lobbying presence remains formidable and the gun movement’s hold on the Republican Party unshaken. Action on key gun issues — universal background checks and a ban on assault weapons, for example — remains stalled because of the narrow partisan divide in the Senate and the 60-vote requirement imposed by the filibuster.

In many Republican-led states, proponents of gun rights hold the upper hand. Gov. Bill Lee of Tennessee, a Republican, signed into law on Thursday legislation allowing most adults in the state to carry a handgun, either concealed or openly, without a permit, background check or training.

Given the wall of Republican opposition, supporters of more restrictive gun laws and regulations applauded even the modest moves that Mr. Biden announced on Thursday, underscoring how their ambitions have been circumscribed by political realities.

“President Biden ran on the strongest gun safety platform in history, and today he proved he’s going to govern like it,” said John Feinblatt, the president of Everytown for Gun Safety.

Other gun control proponents, however, lashed out at Mr. Biden last month, after he said at a news conference that the key to legislative success was ordering priorities, and that infrastructure — not guns — was next on his list.

The president on Thursday outlined several other actions he was taking on his own. He said he would require that when a device known as a stabilizing brace effectively transforms a pistol into a short-barrel rifle, that weapon would be subject to the requirements of the National Firearms Act. That would subject those guns to extra layers of regulation required to own more serious firearms or silencers, including fingerprinting, a background check and a regular renewal of a license.

The gunman in the Boulder, Colo., shooting last month used a pistol with an arm brace, making it more stable and accurate, the president said.

Mr. Biden said the Justice Department would also publish model “red flag” legislation for states. The measure would allow police officers and family members to petition a court to temporarily remove firearms from people who may present a danger to themselves or others.

While the president cannot pass national red flag legislation without Congress, officials said the goal of the guidance was to make it easier for states that want to adopt it to do so now.

“Red flag laws can stop mass shooters before they can act out their violent plans,” Mr. Biden said, noting he wanted to see a national red flag law.

Currently, 19 states and Washington, D.C., have passed their own red flag laws. And while Alaska and Wisconsin are considering passing their own measures, it is not clear how many other states would be interested in doing so — or would find the model legislation useful.

“The math is trickier from here because so many states already have them,” Mr. Heyne said. “Now we’re starting to dip into a different group of states that aren’t even passing background checks.”

Analysts said the model legislation would more likely be used for a state like Connecticut, a leader in gun safety legislation, to update its current laws, rather than for a more conservative state like Wyoming to adopt new measures.

Outside of mass shootings, gun violence remains the leading cause of death for Black men ages 15 to 34, Mr. Biden said in his remarks, noting that additional funding he has proposed for community violence programs can save lives.

“Gun violence in our neighborhood is having a profound impact on our children, even if they’re never involved in pulling the trigger or being the victim on the other side,” he said.

Mr. Biden also announced that the A.T.F. — the embattled agency tasked with enforcing firearms laws — would undertake a new study of criminal gun trafficking, which it has not done since 2000. The study will take into account that modern guns can be made of plastic, printed on a 3-D printer or sold in assembly kits.

The president nominated David Chipman, a supporter of tighter gun rules, to lead the agency, which has not had a permanent director since 2015.

Mr. Chipman, an adviser to the gun control organization founded by former Representative Gabrielle Giffords, is a former agent with the A.T.F. Ms. Giffords left Congress after she was shot in the head in a mass shooting in 2011 in Tucson, Ariz.

While Mr. Chipman’s selection came as welcome news to gun control groups, he faces a potentially difficult confirmation fight in the Senate.

Republicans have effectively hobbled the A.T.F. for decades, often at the urging of the National Rifle Association, which has preferred to keep the agency in a weakened state. The N.R.A. succeeded in lobbying Republicans to have the agency banned from transferring enforcement authority to the F.B.I. or Secret Service and to include limits on unannounced inspections of gun dealers or digitizing its records.

In 2006, lawmakers allied with the National Rifle Association enacted a provision making the position of A.T.F. director subject to Senate confirmation. As a result, only one director, B. Todd Jones, who was nominated by President Barack Obama, has been confirmed over the past 15 years.

The initiatives laid out on Thursday by Mr. Biden show how much more difficult it has become for Democrats to advance their agenda on guns since he served in the Senate. In 1993, Mr. Biden played a key role in the passage of the landmark Brady Handgun Violence Prevention Act, which was named for the onetime White House press secretary James S. Brady, who was shot in an assassination attempt on President Ronald Reagan. A year later, Mr. Biden helped authorize a 10-year ban on assault weapons.

As vice president, he said the worst day in the Obama White House was in 2013, when the Senate rejected the administration’s proposal to expand background checks after the shooting in 2012 at Sandy Hook Elementary School, in Newtown, Conn., that killed 26 people, including 20 children.

Mr. Biden on Thursday acknowledged there was only so much he could do without Congress. “This is just a start,” he said. “We’ve got a lot of work to do,” he added, calling gun violence a “blemish on our character as a nation.”

The House passed two gun control bills last month, but they are languishing in the Senate in the face of the chamber’s 60-vote threshold for passing most legislation, which requires the support of at least 10 Republicans.

“They have offered plenty of thoughts and prayers, members of Congress, but they have passed not a single federal law to reduce gun violence,” Mr. Biden said. “Enough prayers. Time for action.”

Danny Hakim contributed reporting from New York.