* Republican digs heels in despite heavy pressure
* Poll shows Akin still slightly ahead of Democrat McCaskill
* Long list of possible successors if he leaves
By Patricia Zengerle
WASHINGTON, Aug 21 (Reuters) - Congressman Todd Akin, under fire for controversial remarks on abortion and rape, insisted on Tuesday he would not leave the Missouri Senate race, despite pressure from fellow Republicans and talk of who might replace him on the Nov. 6 ballot.
Akin - a staunch abortion opponent - vowed to stay in the contest against Democratic Senator Claire McCaskill, indicating he represents a conservative movement that must be heard.
A 5 p.m. local time (6 p.m. EDT) deadline passed with no indication he planned to take his name off the ballot.
Akin was defiant. His campaign posted a new web site on Tuesday seeking donations with a banner "I'm pro-life and I Stand with Todd Akin." It had briefly featured a picture of a fetus and a picture of McCaskill with U.S. President Barack Obama, but the fetus image was later removed.
"We are going to continue in this race for U.S. Senate," Akin told "The Mike Huckabee Show," a radio program hosted by the former Arkansas governor.
Republican presidential candidate Mitt Romney on Tuesday joined the chorus calling for him to pull out of his race after Akin claimed in a weekend television interview that it was extremely rare for women to get pregnant from "legitimate rape."
"Today, his fellow Missourians urged him to step aside, and I think he should accept their counsel and exit the Senate race," said Romney, who previously condemned Akin's comments.
The outrage over Akin's remarks sent waves of anxiety through the Republican Party a week before it reaches out to independent voters, especially women, at its national convention where it will nominate Romney to run against Obama.
Republicans fear the Akin episode could prevent them from winning in Missouri, lessening their chances of picking up the four seats they need ensure a majority in the 100-member Senate.
McCaskill had trailed Akin by about 10 points but a Public Policy Polling survey on Monday had Akin ahead by 1 point.
WHAT ABOUT JOBS?
To the dismay of many Republicans, Akin's woes have cast a spotlight on a part of the platform party members again endorsed on Tuesday: a call to oppose abortion with no mention of exceptions in cases of rape and incest.
That is not the position of Romney, who has said abortion should be allowed to end pregnancies resulting from rape or incest.
Obama, who supports abortion rights, also strongly denounced Akin's remarks, saying "rape is rape."
Romney's vice presidential running mate, U.S. Representative Paul Ryan of Wisconsin, has expressed a harder line on abortion, saying it should be allowed only to save the life of the mother. The campaign said this week a Romney/Ryan administration would reflect Romney's position.
Ryan, who has co-sponsored anti-abortion legislation with Akin, called the Missouri candidate and suggested he think about leaving the Senate contest. "He thought I maybe should give some thought to stepping down, but he didn't tell me what to do. And that's because he's a very respectful and a very decent guy," Akin said on the Sean Hannity radio program.
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 U.S. senators from the state who urged Akin to step aside.
WHERE TO FIND A WOMAN SUCCESSOR
Under Missouri election law, Akin had until 5 p.m. local time (6 p.m. 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.