WASHINGTON — Representative Todd Akin on Tuesday ignored a deadline to abandon Missouri’s Senate race and vowed to remain the Republican nominee in defiance of his party’s leaders, including the presidential standard-bearer, Mitt Romney.

“I believe the defense of the unborn and a deep respect for life, which underlie all of America, those are important parts of who we are. And they’re not things to run away from,” Mr. Akin said on the radio program hosted by Mike Huckabee, the former Arkansas governor.

Mr. Akin touched off a firestorm of criticism after he said in a television interview on Sunday that in instances of what he called “legitimate rape,” women’s bodies somehow blocked an unwanted pregnancy.

The congressman’s decision to remain in the race against Claire McCaskill, the incumbent Democratic senator, came the same day the Republican Party’s platform committee endorsed a constitutional ban on abortion that does not include an explicit exception for rape.