WASHINGTON -- The White House made clear Thursday that new legislation on gun control will not be on the political agenda this election year, as President Barack Obama and Republican challenger Mitt Romney engaged in their most extensive discussions on the issue since last week's Colorado theatre shootings.

Their comments revived -- if briefly -- a sensitive debate that has faded to the background in national politics and been virtually nonexistent in this year's close presidential race.

While Obama called for tougher background checks on Americans trying to buy a gun, White House spokesman Jay Carney said the president is not pushing for new gun control legislation, though he still supports a ban on assault weapons. Carney said Obama intends to focus on other ways to combat violence.

The White House had faced fresh questions since the Colorado shootings about whether Obama, a strong supporter of gun control while a senator, would make an election-year push for stricter measures. Authorities say the firearms used to kill 12 people and injure dozens were purchased legally.

"A lot of gun owners would agree that an AK-47 belongs in the hands of soldiers, not in the hands of criminals -- that they belong on the battlefield of war, not on the streets of our cities," Obama said in a speech Wednesday to the National Urban League civil rights group.

But gun control is a hotly partisan issue. The powerful National Rifle Association, which fights gun control and has huge sway in Congress, has successfully made the issue nearly off limits among most legislators who fear the group's opposition at re-election time. The Second Amendment of the Constitution guarantees the right to bear arms.

Romney has said changing the nation's laws would not prevent gun-related tragedies.

On Thursday, the Brady Campaign to Prevent Gun Violence challenged both Obama and Romney to lead a search for solutions to gun violence, saying it's shameful for leaders to play politics with the issue when lives could be saved. The group says 32 people are killed by guns in the U.S. each day.

Obama's speech Wednesday acknowledged a national pattern of failing to follow through on calls for tougher gun restrictions after violent crimes.

"Too often, those efforts are defeated by politics and by lobbying and eventually by the pull of our collective attention elsewhere," he said.

Obama pledged to work with lawmakers of both parties to stop violence, including the steady drip of urban crime that has cost many young lives. That's an important issue to the black community, whose turnout in 2008 helped him win the White House.

The president called for stricter background checks for people who want to purchase guns and restrictions to keep mentally unbalanced individuals from buying weapons.

Still, the White House comments Thursday made it clear the Obama campaign wasn't going to take on a gun control issue certain to anger Republicans during a deadlocked campaign centred squarely on the economy.

Romney, pressed on the gun control issue in an NBC news interview during a visit to London, was asked about his tenure as Massachusetts governor, when he signed a bill that banned some assault-style weapons like the type the Colorado shooter is alleged to have used. At the time, Romney described such guns as "instruments of destruction, with the sole purpose of hunting down and killing people."

Asked if he stood by those comments, Romney mentioned the Massachusetts ban but said he didn't think current national laws needed to change.

"I don't happen to believe that America needs new gun laws. A lot of what this ... young man did was clearly against the law. But the fact that it was against the law did not prevent it from happening," he said.