Later, he said on the radio show of Sean Hannity that he sees no harm in continuing to remain in the race.
"My interest in this race has nothing to do with me. It has to do with who we are as a nation," he said. "I think it will help Romney and I think it's going to help the Republican party."
His decision won support from the Missouri Republican Assembly, which issued a statement urging the party to back Akin in the battle against McCaskill.
"The Republican leadership needs to grow a spine and disallow the Democrats, who always support their candidates even when they are wrong, to dictate our stance," the group's statement said. "... While Todd may have been indiscreet in his word choice, he was not wrong in his facts. Todd can win despite this misstep. All Republicans will lose if they continue throwing their candidates under the bus because of a poor word choice."
However, top Republicans strengthened their calls for Akin to depart the race.
"In his heart of hearts, I'm certain that he is sincerely sorry for what he said, but in this instance, when the future of our country is at stake, sorry is not sufficient," Senate Republican leader Mitch McConnell said in a statement. "To continue serving his country in the honorable way he has served throughout his career, it is time for Congressman Akin to step aside."
American Crossroads, an influential conservative super-PAC, also cited the importance of the election, in which McCaskill's seat is considered vital to GOP hopes of gaining a Senate majority.
"Rep. Akin faces a simple choice: Will he help Democrats hold the McCaskill seat and potentially the Senate majority by staying in the race, or will he help Republicans defeat Barack Obama's most reliable ally in the Senate by getting out?" said Steven Law, the group's president and CEO.
Nate Hodson, a spokesman for the Crossroads GPS non-profit that backs Republican candidates around the country, said the group won't spend any more money in the Missouri Senate race for now.
Akin told Huckabee that he still was ahead of McCaskill in the polls, and that pundits had wrongly predicted he would lose in the GOP primary campaign that chose a Senate nominee for the November election.
"We have a message that people understand," Akin said. "It isn't something that's in the brain. It's in the heart."
Voters sounded split over the controversy in Akin's U.S. House district, which comprises a broad swath of suburban St. Louis including formerly rural areas that have seen a large population increase in recent decades.
Gene Wood of St. Charles, about 20 miles west of St. Louis, said he voted for Akin in past elections and the recent Senate primary and still plans to support him.
"It strikes me that this is a tempest in a teapot," Wood said, calling the issue "a matter of semantics."
Another St. Charles resident, Judi Meredith, owns a counseling business that deals with rape victims. She has not supported Akin in the past and said she was horrified by his comments.
"It really showed a level of lack of knowledge and ignorance about society and rape as it's used against women as a tool of oppression," Meredith said, adding she believes Akin should withdraw.
If Akin were to drop out of the race, the state Republican Party would choose another candidate to run against McCaskill, considered one of the most politically vulnerable senators in the country.
Democrats have sought to portray Akin's stance on rape and abortion as indicative of the broader Republican approach to women's issues.
Obama said Akin's remarks were "offensive" and didn't make sense, while House Democratic leader Nancy Pelosi called them "another manifestation of the total disregard and disrespect of women by Republican leaders."
After previously criticizing Akin's remarks, McCaskill issued more supportive comments later Monday.
"While I disagree with what he said, he has now in the last few hours really apologized for what he said," McCaskill noted. "I think what is startling to me is that these party bigwigs are coming down on him and saying that he needs to kick sand in the face of the Republican primary voters."
Amy Kremer, chairwoman of the Tea Party Express, said Tuesday that "the fact that Claire McCaskill wants him to stay in the race speaks volumes."
She said the longer Akin remains in the race, the more his comments will overshadow crucial economic issues.
"What he said is completely indefensible and changes the narrative of what's going on here," Kremer said Tuesday on CNN's "Starting Point with Soledad O'Brien." "If he looks at the bigger picture, he will do what's best and step aside."
Akin was one of the first members of Congress to join the Tea Party Caucus in 2010 and has easily won re-election in recent years. The lawmaker raised $2.2 million this cycle, as of July 18.