March 3 (Bloomberg) -- Former New York Mayor Rudy Giuliani leads Senator John McCain of Arizona, his closest rival for the Republican Party's 2008 presidential nomination, 59 percent to 34 percent in a head-to-head match-up, a Newsweek magazine poll found.

That compares with a statistically insignificant lead of 48 percent for Giuliani to 44 percent for McCain in a January Newsweek poll, the magazine said. Giuliani is ahead 70 percent to 20 percent in a one-on-one contest with former Republican Massachusetts Governor Mitt Romney, Newsweek said.

Of those polled, 82 percent of registered Republicans said a candidate's marital history isn't a significant factor in selecting a nominee, Newsweek said.

The fact that Giuliani has been married three times isn't an important consideration to 75 percent of registered Republicans and to 74 percent of social conservatives, the magazine said.

The poll showed Giuliani in a virtual tie in match-ups against two of the Democrats seeking the 2008 presidential nomination from their party. He leads Democratic Senator Hillary Clinton of New York, 47 to 46 percent, and former Senator John Edwards of North Carolina, 47 to 45 percent, Newsweek said.

Against Democratic Senator Barack Obama of Illinois, Giuliani has a 48 percent to 43 percent lead, the magazine said.

The poll, released today and scheduled for publication in the magazine's March 12 edition, is based on interviews of 1,203 adults on Feb. 28-March 1. The margin of error is plus or minus 3 percentage points.

Most registered Republicans are unfamiliar with Giuliani's position on social issues, with 34 percent of Republicans and 38 percent of social conservatives aware that he favors legalized abortion, the magazine said. And just 16 percent of Republican voters and 15 percent of social conservatives said they know he opposes a constitutional amendment to ban same-sex marriage.

Only 17 percent of Republican voters and 19 percent of social conservatives know that Giuliani supports gun control, Newsweek said.

When sizing up Republican candidates for president, registered Republicans said the two most important issues were the war in Iraq and the economy, with 20 percent saying Iraq was most important and 18 percent saying the economy was their greatest concern.

To contact the reporter on this story: James Tyson at at jtyson@bloomnberg.net

Last Updated: March 3, 2007 14:41 EST