Gun violence dropped dramatically nationwide over the past two decades, but nearly three-quarters of all homicides are still committed with a firearm, the Justice Department said in a report released Tuesday.

The report, by the department’s Bureau of Justice Statistics, painted an encouraging picture of long-term trends at a time of divisive political debate over guns and legislation to regulate them. Firearms-related homicides declined 39 percent between 1993 and 2011, the report said, while nonfatal firearms crimes fell 69 percent during that period.

Yet the document also made clear that when people are killed, it is still most likely to be with a gun. In 2011, as in the past two decades, about 70 percent of all homicides were committed with a firearm, and the majority of those firearms were handguns.

The report is straightforward and highly statistical, and it does not offer any reasons for the decrease in gun violence. Criminologists and other experts have said that explanations for the decline remain elusive, although the Justice Department has in part credited smarter policing practices and investments in law enforcement.

The report, which echoes earlier findings of reductions in violent crime from the FBI’s Uniform Crime Report, comes amid an intense divide over guns, especially since December’s massacre of 20 children and six adults at a school in Newtown, Conn.

Explore a breakdown of gun homicides and gun ownership

Newtown thrust gun control to the top of President Obama’s second-term agenda, and the White House pushed hard for a series of gun-control measures. But the effort unraveled under pressure from the gun rights lobby, and every major proposal was rejected on the Senate floor.

The biggest setback for the White House was the defeat of a compromise measure to expand background checks for firearms purchases. Gun-control proponents have since mobilized to revive the push for stricter laws, but gun rights groups might seize on one finding in Tuesday’s Justice Department report to argue against enhanced background checks.

Senate Democrats said Tuesday that they are eager to turn back to the issue of gun control — but acknowledged it won’t happen anytime soon.

“I don’t know exactly when it’s going to come back exactly on the Senate floor, but I’m very happy that we have some Republicans who are talking out loud that they’d like to take another look at this,” Senate Majority Leader Harry M. Reid (D-Nev.) told reporters.

Less than 1 percent of state prison inmates who possessed a gun when they committed their offense obtained the firearm at a gun show, the report said. Gun shows were central to the measure recently rejected in the Senate: It would have extended the current background-check requirement for firearms purchases from covering only sales at licensed dealerships to any sale that takes place at a gun show or was advertised in print or online.

About 40 percent of state prison inmates obtained their firearms from illegal sources such as theft or through a drug deal, the report said, while 37 percent got their guns from a family member or friend. Those findings are based on data from 2004.

Overall, the Justice Department report said, firearm-related homicides dropped from 18,253 homicides in 1993 to 11,101 in 2011, while nonfatal firearm crimes declined from 1.5 million in 1993 to 467,300 in 2011. The drop extended to schools: Homicides at schools declined from an average of 29 per year in the 1990s to an average of 20 per year in the 2000s.

Although the rate of firearm homicides for African Americans declined by 51 percent over the past two decades, that rate was still 14.6 per 100,000 people in 2010 — compared with 1.9 for whites.

In 2010, the South had the highest rate of firearms homicides nationwide at 4.4 per 100,000 people, the report said. That compared with 3.4 in the Midwest, 3.0 in the West and 2.8 in the Northeast.

Reid said he met with voters in Nevada last week who “shook their heads in dismay that the Republicans here in Congress . . . feel that if someone has deep, severe mental problems they should be able to buy a gun. Or that someone who’s a criminal should be able to buy a gun.”

Reid was referring to the defeat of a bipartisan plan authored by Sens. Joe Manchin III (D-W.Va.) and Patrick J. Toomey (R-Pa.) that would have expanded the national gun background check system to include most commercial firearms sales. He added that Sen. Jeff Flake (R-Ariz.), among others, is open to talking again about the issue.

But Flake said he’s not reconsidering his vote against the proposal.

“I think they ought to go back to the drawing board,” Flake told reporters, adding that he’s concerned that the Manchin-Toomey plan too broadly defined the parameters of commercial gun sales. “Virtually anything that touches the Internet — text messages, any posting — is a commercial sale. That’s far, far too broad,” he said.

Discuss this topic and other political issues in the politics discussion forums.