ABC News' Michael Falcone reports:

TAMPA, Fla. - He was perhaps Mitt Romney's most bitter enemy during the protracted Republican presidential primary, but on Tuesday night Rick Santorum plans to give his most hearty pat on the back yet to a former rival he spent the better part of a year slapping in the face.

In his Republican National Convention speech, Santorum plans to take up the Romney campaign's line of attack on President Obama's handling of welfare reform, talk about getting Americans back to work and highlighting the conservative principles he campaigned on during his own presidential bid.

Romney campaign strategist Russ Schfriefer said he had read the former Pennsylvania senator's speech and that it was "particularly good. Another source familiar with the text said it "will tug at your heartstrings."

Schriefer said Santorum would draw heavily from his own biography as the hard-working product of immigrants and speak about the "dignity of work."

"I would cast it as a hopeful," Santorum confidante John Brabender told ABC News in an interview. But he acknowledged that the former presidential hopeful would not be pulling any punches.

Brabender said Santorum viewed Obama's handling of welfare as "very illustrative of the failure of his presidency."

In the speech, 90 percent of which Brabender said Santorum wrote himself, he "contrasts what he believes this country was built on vs. Barack Obama and how the two seem to be dramatically opposed."

Sources indicated that Santorum had been upgraded to a more coveted speaking slot at about 9:15 p.m. after originally being assigned an earlier one. His remarks are expected to clock in at about 14 minutes.

But Santorum's role in Tampa this week goes far beyond his brief time at the podium in the convention hall on Tuesday night. He is also embracing a role he begun carving out during the primaries - as one of most prominent leaders of the conservative movement.

Santorum has put together a "Patriots for Romney-Ryan 2012? reception in Tampa's Liberty Plaza on Wednesday featuring a who's who of the conservative movement, including Family Research Council head Tony Perkins, Americans For Tax Reform's Gorver Norquist, the Faith and Freedom Coalition's Ralph Reed, Susan B. Anthony List president Marjorie Dannenfelser and such conservative luminaries as Gary Bauer, Phyllis Schlafly and Richard Viguerie.

Some of these leaders publicly backed Santorum over Romney during the primary. In fact, after he dropped out of the race Santorum's own loyalty to Romney appeared to be in doubt when it took weeks for him to endorse the presumptive Republican nominee. Since then he has only campaigned for Romney a handful of times.

But now that Romney has officially become the nominee of the party, Brabender said Santorum's conservative credentials and his blue-collar roots could be an asset between now and November.

"We have to turn some conservatives from just being Romney voters to being Romney activists," he said. "What is clear is that when he speaks, conservatives listen."

And although he has, at times, been critical of Romney's policies, Santorum loyalists said those differences would not be on display this week.

"This is Mitt Romney's convention and Rick understands that," former Santorum campaign communications director Hogan Gidley said in an interview with ABC News. "His speech will bolster the nominee's argument that he's the best person to lead this nation forward."