WASHINGTON — In the emotional statement on the Newtown shootings that President Obama delivered from the White House on Friday, it was a single line, spoken as much in anger as in grief, that stood out. The words were cautious and were immediately criticized for being too timid. But they may have signaled that the long-dormant debate over the nation’s gun laws is about to be re-engaged.

“We’re going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics,” Mr. Obama said, listing the devastation wrought by other gun violence, from a recent attack in an Oregon shopping mall to the shootings in a movie theater in Aurora, Colo., in July.

But Mayor Michael R. Bloomberg of New York spoke for many gun-control advocates, who have been frustrated and disappointed by Mr. Obama’s failure to embrace the issue, when he said he wanted to hear much more.

“Calling for ‘meaningful action’ is not enough. We need immediate action,” said Mr. Bloomberg, who is a leader of a group of mayors against illegal gun ownership.