By Susan Heavey
WASHINGTON (Reuters) - A new poll Monday showed Mitt Romney is surprisingly strong in two Republican presidential primary contests in the South this week that are crucial to his conservative rivals Rick Santorum and Newt Gingrich.
"About all we know for sure about Tuesday's primaries is that Ron Paul will finish last in them," Dean Debnam, president of Public Policy Polling, said in releasing the results. "Beyond that it's plausible that any of the candidates could finish between first and third in both Alabama and Mississippi."
In Mississippi, Gingrich has a slight lead with 33 percent, while Romney has 31 percent, Santorum 27 percent and Paul 7 percent in the race to become the Republican challenger to Democratic President Barack Obama in November.
In Alabama, the race is tighter, with Romney, a former governor of Massachusetts, at 31 percent, Gingrich at 30 percent, Santorum at 29 percent and Paul, a U.S. representative from Texas, at 8 percent.
Both Gingrich, a former congressman from Georgia, and Santorum, a former U.S. senator from Pennsylvania, are staking their candidacies on their conservative credentials.
Front-runner Romney had been seen as too moderate to win one of this week's primaries in the heart of the conservative South but he has gained momentum from a series of primary wins in recent weeks.
Both Gingrich and Santorum have urged each other to step out of the race to coalesce votes among more conservative Republicans.
According to Public Policy Polling's findings, the two rivals are both more popular than Romney in the two southern states that vote on Tuesday.
The group conducted its telephone survey on Saturday and Sunday. Its Mississippi poll had 656 likely Republican voters and a margin of error of plus-or-minus 3.8 percent. Its Alabama survey has 600 likely Republican primary voters and a margin of error of plus-or-minus 4 percent.
Santorum on Monday defended the drawn-out Republican battle for a nominee and a potential showdown at the party's convention in August.
"If we have continued contested primaries going through this, we're going to see very shortly that the conservative in this race is going to rise," he said on NBC's "Today" program.
"It's a conservative party ... if the opportunity provides itself in an open convention, they are not going to nominate a moderate Massachusetts governor," he said.