President Obama promised Wednesday to lead a national discussion about gun control after the deadly mass shootings last week in Colorado, wading into the gun issue more extensively than at any other time in his presidency.

Even this week, White House press secretary Jay Carney indicated that the president was unlikely to push for new gun legislation, citing persistent opposition in Congress. But Obama told the National Urban League here that he believes a lot of gun owners would agree that “AK-47s belong in the hands of soldiers,” not civilians on American streets.

The president called the Aurora massacre an “extraordinarily heartbreaking tragedy.” But, he added, talk of reforming gun laws after similar mass shootings has too often been “defeated by politics and by lobbying and eventually by the pull of our collective attention elsewhere.”

Obama’s speech seemed sure to intensify the debate on gun control. The president’s comments were striking because he has generally been cautious on the politically potent issue of firearms — to the point that some prominent politicians and advocates had criticized him, accusing him of barely addressing gun regulations in the immediate aftermath of the massacre in Aurora.

Obama’s opponent in the presidential election, Mitt Romney, weighed in earlier Wednesday, saying that he saw no need for new gun restrictions after the Colorado rampage, allegedly carried out by a failed graduate student who used an assault rifle, a Glock semiautomatic handgun and a shotgun.

“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,” Romney told “NBC Nightly News” anchor Brian Williams in an interview taped in London as he embarked on a week-long foreign trip.

Romney acknowledged that as governor of Massachusetts he supported a bill that banned assault weapons, but he said he opposed a similar measure for the rest of the country.

“We can sometimes hope that just changing a law will make all bad things go away. It won’t,” Romney said. “Changing the heart of the American people may well be what’s essential to improve the lots of the American people.”

Obama gave few specifics Wednesday evening about what changes, if any, he might seek on guns, although his reference to AK-47s was sure to hearten advocates of an assault-weapons ban like the one passed during the Bill Clinton presidency, which expired in 2004. The current president, however, hasn’t advocated such a measure.

In his speech, Obama declared gun violence a national tragedy that reaches beyond mass shootings such as those in Aurora and in Tucson — where six people were killed and 13 wounded, including Rep. Gabrielle Giffords, in a January 2011 attack — and into the lives of innocent people struck down by criminals every day.

“For every Tucson or Aurora, there is daily heartbreak,” Obama said. “Violence plagues the biggest cities, but it also plagues the smallest towns.”

Obama said that laws should be better enforced and that guns should be kept out of the hands of people with mental illness. Although he reiterated his commitment to uphold gun owners’ Second Amendment rights to responsibly bear arms, he blamed Congress for inaction on what he called common-sense restrictions to keep guns out of the hands of criminals.

Well-funded gun-rights organizations such as the National Rifle Association exert great power in Congress, and public-opinion polls show that a declining number of Americans feel the need for stricter gun laws.