ABC News' Shushannah Walshe and Michael Falcone report:

FLORENCE, S.C. - Presidential candidate Rick Santorum plans to open the final week of campaigning before voters go to the polls in South Carolina with his strongest assault yet on rivals Mitt Romney and Ron Paul.

Aides to Santorum told ABC News on Sunday that the former Pennsylvania senator is fed up with the negative attacks coming from the campaigns of those two opponents and from their allies. He will hold a press conference to make his displeasure known after his first campaign event of the day on Monday.

"It's time for these negative, false attacks to stop - enough is enough," Santorum's communications director Hogan Gidley said in an interview with ABC News. "Mitt Romney and Ron Paul both tried these kinds of tactics in other states and they tried these same type of tactics four years ago. It's time for Rick to set the record straight and tomorrow he will."

Gidley complained specifically about mailers and robocalls "bashing Rick and distorting his record" on a variety of issues. He said his candidate  will deal with those attacks "head on" following a town hall meeting he will hold early Monday morning at Lizard's Thicket restaurant in Columbia, S.C.

Santorum previewed the fresh offensive at his second and final campaign stop on Sunday, criticizing the pro-Romney super PAC, Restore Our Future, for running an ad that hits him on earmarks and accuses the former senator of voting to give convicted felons the right to vote. (The ad also began running in Florida this week.)

He told a crowd of about 200 at a restaurant in Florence, S.C. that he expects those kind of campaign tactics from President Obama, but "I don't expect that from a Republican running for president." He added that purposely misleading the voters of South Carolina" is "just yuck."

"There is enough that Barack Obama has done that we don't have to make up things," he said. "I know a lot of candidates have been very upset about Governor Romney and his PAC and what he's doing attacking."

He accused both Romney and Paul of running "a pretty hard negative campaign, which I think tells you a little bit about what they think of their ability to appeal to people's better sides that they have to go out there and just hammer everybody out there."

He called the Restore Our Future ad's portrayal of his support for giving felons the right to vote a "lie." He said he only supported the right for felons "who served their time, came out of jail, had served their parole and probation."

"We are better than that," Santorum said to those gathered Sunday afternoon at Percy & Willie's Food & Spirit in Florence.

In offering his pitch to South Carolina voters, he jabbed Romney for his health care plan in Massachusetts saying that it renders Romney unqualified to be the nominee.

"Why would the people of South Carolina put out there someone who we lose that issue with?" Santorum asked the audience. "For all the things that Governor Romney has flip-flopped on the one he should have is this one  - and it's not the contrast we need, folks."

Although he focused much of his fire on Romney, he also went after President Obama with some of his strongest language yet. He said the president "encourages the division" in this country and that was "beneath the dignity" of his office.

"The 99 versus the one, this class against this class, this ethnic group against this ethnic group, this racial group, this labor group," Santorum said."It's constantly pitting one group against another all for someone political purpose. It's disgusting."

After receiving the backing of key evangelical leaders this weekend, Santorum is tailoring his closing argument to appeal to social conservative voters in the Palmetto State in an attempt to draw the majority of their support to his candidacy, an approach that is likely his only chance to either catch up or overtake Romney.

"What I hear all the time, even from our side of the aisle, some on the Republican side, 'Well we need to put these social issues aside. All we need to worry about is economics, cutting taxes, cutting spending and everything will be fine,'" Santorum complained. "They don't know America. If all you think we need to do to get this economy going and get this country on the right track is to cut government, and reduce taxes, you don't understand America."

"America is a moral enterprise, not an economic enterprise," Santorum to cheers and at least one "Amen" from the South Carolina crowd.