Sen. Patrick Leahy (D-Vt.), who chairs the Senate Judiciary Committee, said he plans to field ideas from a broad range of voices before advancing any gun-control legislation through the committee. (Linda Davidson/The Washington Post)

President Obama has promised quick action to get a series of gun-control proposals through Congress and has been moving purposefully to that end.

But one of his key allies on Capitol Hill, Sen. Patrick J. Leahy (D-Vt.), could prove to be an early obstacle to the president’s swift pace.

Leahy, who chairs the Senate Judiciary Committee and will be at the White House on Wednesday when Obama unveils proposals from Vice President Biden to limit gun violence, said he wants to hear from more than just the administration. Leahy said he plans to field ideas from a broad range of voices before advancing any legislation through the committee.

“I want everybody to be heard,” Leahy said in an interview Tuesday, despite potential pressure from the White House to act quickly. “I have some ideas of things that can be done, and if there are things in the vice president’s proposal that the committee agrees with, then they’ll be included in the legislation. If not, they won’t be.”

Leahy’s decision to remain at the helm of the Judiciary Committee, instead of seeking the powerful Appropriations Committee gavel, was greeted with disappointment by some gun-control advocates, who worry his centrist views on gun issues will make him an insufficient advocate for bold action. Advocates blame Leahy for stalling efforts to push new restrictions after the shooting rampage two years ago that injured then-congresswoman Gabrielle Giffords (D-Ariz.).

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“What I’m really afraid of is he’s going to be too cautious in his approach,” said Joshua Horwitz, executive director of the Coalition to Stop Gun Violence. “It would have been great to have one of our staunch allies in that position.”

But Leahy insisted that he is approaching the coming gun debate with decades of political and real-world experience. “I’m one of the most effective legislators, and nobody’s gotten more legislation through than I have,” he said, later adding: “I’m a gun owner. I know a lot about it. I was a champion marksman in college. I have a pistol range behind my house.”

With gun control and immigration reform promising to dominate Obama’s domestic agenda in the coming months, Leahy’s thinking and how he approaches the various pieces of legislation in his committee will be crucial to the outcomes on both issues. He also expects to preside over one or more Supreme Court nominations in the next four years.

Leahy, 72, has chaired Judiciary since 2007 and had the option last month of leaving to head Appropriations after the death of its chairman, Sen. Daniel K. Inouye (D-Hawaii). But the Vermont senator — a former lawyer and state prosecutor — said that sticking with Judiciary “allows me to stay involved with where my passions are.” In addition, Leahy will maintain his senior position on Appropriations. “There’s nothing I want for Vermont that I’m not going to be able to have,” he said.

Leahy said he plans a series of hearings on gun control that will include input from the National Rifle Association, law enforcement groups, educators and concerned parents.

“I’m not interested in anybody for or against gun ownership who will come in and just give me polemics,” he said. “I want some real things.”

Leahy said that he was not in a position to handicap the chances of any single proposal and that he could not gauge whether Senate Majority Leader Harry M. Reid (D-Nev.) was correct in suggesting recently that there was little chance of Congress passing an assault weapons ban.

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.

Peter Wallsten contributed to this report.