The actor Matthew McConaughey, a native son of Uvalde, Texas, took the lectern in the White House briefing room on Tuesday and spoke of learning, in his boyhood, “to revere the power and the capability” of a gun.

He then told of the horror he felt at losing 19 school children in his hometown to a man with a rifle so high-powered that it disfigured many of their bodies beyond recognition.

Fresh off a meeting with President Biden, Mr. McConaughey echoed the president’s call for expanded background checks on gun buyers, new “red flag” laws

and additional restrictions on the purchase of AR-15 rifles like the one used to kill 19 children and two teachers at an elementary school in Uvalde last month.

He cast himself as a voice for responsible gun owners and described, in graphic detail, the horrors of gun violence.

The shooting is one of the deadliest school attacks on record and one of more than 200 mass shootings recorded in the United States so far this year.

Mr. McConaughey’s appearance at the White House came as a bipartisan group of senators tries to negotiate new legislation to respond to gun violence.

Senators involved in the talks expressed muted optimism that they could produce some sort of legislation that might clear the evenly divided chamber, though it was certain to fall short of some measures,

Mr. McConaughey, who also met with lawmakers on Capitol Hill on Tuesday, said that he and his wife, Camilla, had gone to Uvalde the day after the shooting.

He choked up as he spoke of meeting the parents of Alithia Ramirez, 10, who dreamed of going to art school in Paris, and how Alithia’s father, Ryan, had recently secured a higher-paying job, promising it meant that he would spoil her by taking her to Sea World.