‘‘I am also betting that the majority, the vast majority, of responsible, law-abiding gun owners would be some of the first to say that we should be able to keep an irresponsible, law-breaking few from buying a weapon of war,’’ Obama said.

The president challenged the National Rifle Association, the country’s most powerful gun lobby and key backer of many Republican politicians, to join the broader effort to reduce gun violence as well.

‘‘Hopefully they'll do some self-reflection,’’ Obama said of the NRA.

The NRA made its first comments since the Newtown shooting on Tuesday, promising to offer ‘‘meaningful contributions to help make sure this never happens again.’’

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