But Leahy said that he supports Obama's use of executive action to bolster federal background checks and that Congress should improve how the nation cares for the mentally ill.
In a speech Wednesday at Georgetown University's law school, Leahy plans to call for measures to limit children's exposure to violence in video games and movies.
"As President Obama has made clear, no single step can end this kind of violence," Leahy is expected to tell law students, according to prepared excerpts provided by his office. "But the fact that we cannot do everything that could help should not paralyze us from doing anything that can help."
Leahy said he is most interested in closing the "gun-show loophole" that permits people to purchase firearms at private gun shows without undergoing background checks. He noted the frustrations of his local gun shop owner, who has to pay fees and endure strict reporting requirements that private dealers easily avoid.
"I think the majority of people would agree that whatever the requirements are for buying a gun, they should be the same no matter where you buy it," Leahy said. "That's the area we'll look into."
Leahy, who has served in the Senate since 1975, succeeded Inouye as president pro tempore, the most senior member of the majority party. Now third in line to the presidency, he is still adjusting to life with a full-time security detail, aides said.