In 2020, amid the disruptions of the pandemic and the social upheaval following the police murder of George Floyd in Minneapolis, the United States saw the largest increase in its homicide rate in modern history. Now, more than three years after the start of the pandemic, the country is on track to record one of its largest — if not the largest — annual declines in homicides, according to a report released on Thursday.

Even so, violent crime is still considerably higher than just before the pandemic, the benchmark that police chiefs and city leaders are striving to return to, as cities remain awash in guns.

In the new report, the nonpartisan Council on Criminal Justice examined crime data from 30 U.S. cities — including Chicago, Los Angeles, New York, Philadelphia and Denver — and found that through the first half of the year there were 202 fewer homicides, a drop of more than 9 percent. Still, homicides across those cities are 24 percent higher than in same period of 2019.

“I would call the result heartening,” said Richard Rosenfeld, a professor of criminology and criminal justice at the University of Missouri-St. Louis who was the lead author of the report. “Not a cause for celebration. Most cities have not returned to the homicide levels that were prevailing just prior to the height of the pandemic. So we have a ways to go.”

The latest data at least offers a hopeful sign that the increases in violent crime during the pandemic were not the start of a new era of steadily rising crime, as many experts have worried. But the data is limited to the cities in which the council could obtain data, and the authors cautioned that for some categories only a few cities released statistics.

Gun assaults, for instance, declined 5.6 percent — a positive sign for gun violence overall — but that was based on only the 10 cities in the study that provided gun assault data. Robberies, burglaries and larcenies were also down. Car thefts, which have risen substantially in recent years, partially because of the ease in which teenagers have been able to steal Kia and Hyundai models, rose even further.

The council began tracking crime at the start of the pandemic, seeking to provide a timely snapshot of national trends and fill the void in comprehensive data from government agencies. The F.B.I., which typically releases national statistics in the fall for the prior year, has been hampered by a shift in 2021 to a new reporting system that saw several large cities, such as Chicago and New York, fail to submit data.

Just as criminologists struggle to reach a consensus to explain sudden increases in crime like the United States saw in 2020, concrete explanations for declines in crime are similarly elusive.

“It’s like explaining the score at halftime,” said Jeff Asher, a crime analyst based in New Orleans who tracks homicides across American cities and levels of law enforcement staffing. “Even if you are up by two touchdowns, it’s still halftime. And so understanding that context makes it hard to say, ‘Oh it’s because it’s x, y or z.’ We don’t have a strong understanding yet. And it’ll be a little while until we do have an understanding.”

But many agree that the disruptions of the pandemic — the social isolation, the closure of schools and jobs lost — likely led to an increase in crime. More contentious is an unproven theory cited by some experts that amid the social unrest that followed the murder of Mr. Floyd, officers in some places pulled back from enforcement and some citizens, distrustful of law enforcement, stopped working with police.

Notably, violent crime has fallen at a time when many police departments are smaller than they were before the pandemic. While the defund the police movement, which grew out of the Floyd protests, lost momentum as crime rose, police staffing levels declined in many cities as officers retired or quit and as many departments struggled to recruit new officers in a competitive U.S. job market. The result for some major cities has been an unintended experiment in what a smaller police department looks like.

Los Angeles, for example, is down about 1,000 officers since 2019 — it had about 9,200 officers at the end of last year — and hundreds of civilian workers. And yet homicides are down more than 20 percent this year, and overall gun violence has fallen at a similar clip.

“We are still not done with getting back to crime levels, community safety levels, that we saw just four years ago,” Chief Michel Moore of the Los Angeles Police Department said in an interview. He added: “We’re not home free because of the persistence of gun violence, and the persistence of too many guns in too many hands.”

With fewer officers, Mr. Moore said the department was relying on overtime and on focusing resources on the most serious violent and property crimes. He said that the department was not responding as quickly as it used to for lesser issues, like neighborhood disputes or loud, late-night parties. The department’s goal is to hire 700 more officers and 300 more civilians this year.

“The service levels have been impacted,” he said, adding that the change has come at the expense of community members who typically interact with the police only on that type of lower level issue. That “gives me concern because it undermines their sense of confidence and their sense of safety in the department, and in government,” he said.

A similar dynamic of smaller departments and falling crime has also played out in Philadelphia, which had about 5,800 officers at the end of last year, more than 700 fewer than in 2019. The city saw homicides decline more than 20 percent and has spent millions of dollars in overtime.

In Minneapolis, whose homicide data is not included in the council’s report, violent crime is also down substantially, and the department has about 300 fewer officers than in 2019. To maintain the reductions in crime, the department has said it would focus its limited resources this summer on crime hot spots in the city.

Even with the increases in recent years, violent crime is still far below its historical peaks reached in the early 1990s. In periods of the last century when murders and violent crime surged, policymakers responded with ever harsher criminal justice policies: mandatory minimum sentences for drug crimes, tough new laws for juvenile offenders and massive increases in policing, all of which led to mass incarceration.

And as crime rose in recent years, some mayors and governors did respond with tough-on-crime rhetoric. But, at least so far, there have not been major policy shifts toward more punitive measures like during the 1980s and 1990s, said Jeffrey A. Fagan, an expert on crime and policing at Columbia Law School. Efforts to overhaul bail systems are continuing and progressive prosecutors are being elected in many cities, which, he said, “showed that you really didn’t need these harsh measures that were put in place to have violence rates and murder rates decline.”