Updated

Former New York City Mayor Rudy Giuliani and Arizona Sen. John McCain are the clear leaders among Republican hopefuls in the South Carolina primary. Former Mass. Gov. Mitt Romney is the only other candidate to receive double-digit support, according to a new FOX News poll.

Opinion Dynamics Corp. conducted the telephone poll of 600 likely South Carolina Republican primary voters for FOX News from April 1 to April 3. There is a margin of error of plus or minus 4 percentage points for results based on the entire sample.

The poll finds that Giuliani receives the backing of 26 percent and McCain 25 percent of South Carolina Republican primary voters. Romney has the support of 14 percent.

In the next tier of candidates, 5 percent of likely voters say they will support former House Speaker Newt Gingrich, which is most notable because voters volunteered his name even though he is not an announced candidate and therefore was not included in the list of vote choices read.

Click here to see full results of the poll.

All other candidates receive the support of 2 percent or less, and 16 percent are undecided.

Men are slightly more likely to support Giuliani (28 percent) over McCain (21 percent), while among women McCain (29 percent) has the edge over Giuliani (24 percent).

Born-again Christian voters split their support between Giuliani (25 percent) and McCain (25 percent), with about one of 10 backing Romney (13 percent).

The South Carolina Republican Party is expected to hold its presidential primary in early February 2008.

Given that voting in the primary is about 10 months away, many voters — 62 percent — say they may change their mind about which candidate to support. Three in 10 voters (30 percent) say they are certain to support their current choice.

Among Giuliani voters, 35 percent say they are certain to vote for him in the primary, while 30 percent of McCain voters and 20 percent of Romney voters say their mind is already made up.

Despite there being 10 announced Republican contenders, there is little satisfaction among voters with their choices. Only 7 percent say they are "extremely" satisfied and 16 percent "very" satisfied with the choice of candidates in the primary. Twice as many say they are either "somewhat" (41 percent) or "not very" satisfied (28 percent).

• Click here to visit FOXNews.com's You Decide 2008 center for more coverage.

FOX News and the South Carolina Republican Party will jointly host a 2008 presidential debate of top Republican contenders on May 15, 2007.

The most important issue to South Carolina voters in the GOP primary election is crystal clear: Iraq. Almost four in 10 voters (37 percent) say Iraq is the top issue to their vote — more than five times as many as cite any other issue.

Fully 70 percent of South Carolina Republican primary voters approve of the job George W. Bush is doing as president, and 75 percent support the war in Iraq, including 47 percent that "strongly" support the war.