HARTFORD — President Obama came here on Monday before a roaring, enthusiastic crowd to remember the tragedy of 20 children and 6 educators slain at Sandy Hook Elementary School and put new pressure on a recalcitrant Congress to honor them with gun-control legislation.

In an impassioned speech that at times took on the tone of a campaign rally, Mr. Obama told an audience of 3,100 at the University of Hartford that he came to Connecticut to ensure that the deaths in the school in Newtown would not recede and to remind Americans how important their voice is as the gun debates unfold.

“If you’re an American who wants to do something to prevent more families from knowing the immeasurable anguish that these families here have known, then we have to act,” Mr. Obama said. “Now’s the time to get engaged. Now’s the time to get involved. Now’s the time to push back on fear and frustration and misinformation. Now’s the time for everybody to make their voices heard, from every statehouse to the corridors of Congress.”

But as Mr. Obama spoke, Republicans on Capitol Hill were threatening to prevent a gun-control measure from even coming up for debate.