The controversy is a distraction in a campaign Romney has sought to keep tightly focused on the economy and jobs.

Tim Wildmon, president of the influential American Family Association, was one of several social conservatives who have come to Akin's defense.

"This is a decent, honorable man who has been pro-life and pro-traditional values. He has apologized for his choice of words and that should be the end of it," Wildmon said.

Although religious conservatives are a crucial part of the Republican base, many party leaders say its central message should be its conservative approach to fiscal issues like debt and deficits.

"It's not that we keep shooting ourselves in the foot. We keep shooting ourselves in the eyes," said former Missouri Senator John Danforth, one of a group of current and former US senators from the state who urged Akin to step aside.

WHERE TO FIND A WOMAN SUCCESSOR

Under Missouri election law, Akin had until 5 pm local time (6 pm EDT) to get his name off the ballot for the Nov 6 election most easily. But he faces a harder deadline on Sept 25, the last day his name can be removed with a court order.

If Akin withdraws, the Missouri Republican committee would name a successor to run against McCaskill. Possible candidates include the two Republicans Akin defeated in the primary just two weeks ago - St. Louis businessman John Brunner and former state Senator Sarah Steelman.

But the party can pick any candidate.

Other possibilities include former Senator Jim Talent, who lost narrowly to McCaskill in 2006 and Representative Jo Ann Emerson, considered a favorite because many Republicans think the party would best reassure women voters by running a woman.

In another sign that he is not leaving, US News and World Report reported that Akin spent $150,000 on Tuesday for television advertisements in seven media markets.

But he will struggle to keep up with McCaskill, especially after the Karl Rove-linked American Crossroads Super PAC and the Republican Senate committee said they would hold back millions in funding earmarked for the race.

McCaskill's campaign is using Akin's comments in its fundraising. Emily's List, which supports Democratic women candidates, said it has seen a big jump in fundraising.

Akin apologized again in an Internet advertisement called "Forgiveness." And he sent a fundraising letter to supporters on Tuesday asking for donations of $3 or more.