Businessman Herman Cain and former Massachusetts governor Mitt Romney are running nearly even atop the field of 2012 GOP presidential hopefuls, a new Washington Post-ABC News poll shows, with most Republicans dismissing the harassment allegations that over the past week have roiled Cain’s campaign.

Seven in 10 Republicans say reports that Cain made unwanted advances toward two employees when he was head of the National Restaurant Association in the 1990s — allegations which have been stiffly rebutted by Cain’s campaign — do not matter when it comes to picking a candidate.

But the potential threat to his burgeoning campaign is evident as well, with Cain slipping to third place among those who see the charges as serious, and Republican women significantly more likely than men to say the scandal makes them less apt to support Cain.

The poll was conducted Oct. 31 through Nov. 3, starting the evening after Politico first reported the harassment allegations. Support for Cain was basically steady over the four nights of interviewing, even as new charges against him surfaced.

Nearly a quarter of all Republicans and GOP-leaning independents now back Cain as the party’s nominee, his best showing in Post-ABC polls this year, and up significantly from early October. At 23 percent nationally, Cain is neck-and-neck with Romney (24 percent) atop the GOP field.

“I think [the charges against Cain are] mostly garbage that they throw at people who want to be president,” James Kindsch, from Middleton, Wis., said in a follow-up interview.

“I don’t believe it,” said Paul Bradley from Fishersville, Va., adding: “The further in the past they happened, the less accurate they are.”

In the poll, a majority of Republicans — 55 percent — see reports of Cain’s alleged misconduct as “not a serious matter,” and 70 percent say the situation makes no difference in their vote.

At the same time, there is clearly a risk to Cain’s campaign should the allegations stick: Sizable numbers of Republicans (37 percent) and GOP-leaning independents (42 percent) see the allegations against Cain as serious ones. In this combined group, Romney is well ahead, with 31 percent support. Cain slips numerically into third place, behind Texas Gov. Rick Perry.

Among the possible beneficiaries of a shift away from either of the two front-runners are Perry, who checks in at 13 percent in the new poll (down from an early September high of 29 percent) and former House speaker Newt Gingrich, who polled at 12 percent, reaching double digits for the first time this fall.

Texas Rep. Ron Paul is at 8 percent, Minnesota Rep. Michele Bachmann is at 4 percent, and former Utah governor Jon Huntsman Jr. and former Pennsylvania senator Rick Santorum are both at 1 percent.

Although Republican men and women have similar views about whether the allegations against Cain represent a serious matter, GOP women are about twice as likely as men to say the whole situation makes them less apt to vote for Cain (25 to 12 percent).

“He’s a homey person,” said Blair Watkins of Raleigh, North Carolina, who leans toward Cain but expressed reservations about the sexual harassment allegations in a subsequent interview: “You need someone who’s coming in with a clean record.”

Although Cain remains a leader in the presidential race, it is unclear whether he would have scored even higher in the new poll absent the allegations. A Quinnipiac poll launched before the scandal broke and ending Monday had Cain at 30 percent among registered voters, up from 17 percent in early October (he also polled at 17 percent in a Post-ABC poll in early October).

Among registered voters in the new Post-ABC poll, Cain is at 23 percent, just as he is among all Republicans and GOP-leaning independents. (Romney is at 25 percent among registered voters.)

One shift in Cain’s support over the past month might help him build momentum: His base has diversified, extending to non-tea-party Republicans. The businessman leads Romney among strong tea party backers, but his support has jumped from 1 percent to 14 percent over the past month among those who do not support the movement.

In a sign of potential uncertainty ahead, however, just 27 percent of Cain’s supporters say they will definitely vote for him. A similarly low number of Romney’s supporters — 28 percent — say they are certain to stick with their choice.

A total of 1,004 telephone interviews were conducted, including a sample of 438 Republicans and GOP-leaning independents. The margin of sampling error for this smaller sample is plus or minus 5.5 percentage points.

Polling manager Peyton M. Craighill and polling analyst Scott Clement contributed to this report.