WASHINGTON (Reuters) - Newt Gingrich holds a 10-point lead in the fight for the Republican presidential nomination, but he would fare worse against President Barack Obama than Republican Mitt Romney, according to a new Reuters/Ipsos poll.

With the first nominating contest in Iowa less than three weeks away, Gingrich leads Romney among Republican voters nationwide by 28 percent to 18 percent, the poll found.

However, the poll raises questions about whether Gingrich -- a former speaker of the U.S. House of Representatives who has shot to the top of Republican opinion polls in recent weeks -- would be able to defeat Obama.

The poll found that if the November 2012 presidential election were held today, Obama would defeat Gingrich, 51 percent to 38 percent. By contrast, Obama would defeat Romney by a narrower margin, 48 percent to 40 percent.

Analysts say the results reflect the risk that Republicans could face if they nominate Gingrich, whose strong performances in debates have won him support among conservatives seeking an alternative to Romney.

Gingrich has a long record of making provocative statements that could alienate independent voters, such as when he recently referred to Palestinians as an "invented" people.

Even so, some conservative Republicans see him as preferable to Romney, a former Massachusetts governor who has built a more extensive campaign and fundraising operation.

"This is the Republican dilemma," said Calvin Jillson, a political science professor at Southern Methodist University. " 'Do I want to enjoy myself by voting for Gingrich ... or do I want to look toward the general election and see a winnable contest?'"

Romney has been widely viewed as the candidate to beat among Republicans.

Obama's campaign was focused squarely on an eventual race against Romney until this week, when it began taking shots at Gingrich -- an acknowledgement of the former speaker's elevated standing in the Republican race.

The new poll found Texas Representative Ron Paul and Texas Governor Rick Perry tied for third place with 12 percent each, while Minnesota Representative Michele Bachmann has the support of 10 percent of Republicans.

Former Utah Governor John Huntsman is next with 5 percent, followed by former Pennsylvania senator Rick Santorum, with 4 percent. Another 4 percent picked other candidates or none at all.

The poll, taken from December 8 to December 12, shows Gingrich's remarkable comeback since a staff mutiny and criticism by fellow Republicans nearly torpedoed his campaign in June. A Reuters/Ipsos poll taken during that period showed him polling at 6 percent.

The poll also found that Obama could be making a comeback of sorts as the economy shows signs of improvement and Republican candidates bloody each other in a series of televised debates.

Obama's 8 point lead over Romney is a dramatic increase from the 1 point deficit he faced in a Reuters/Ipsos poll taken from October 31 to November 3.

Although Obama is doing better compared with Republicans, his approval rating, at 47 percent, is little changed since the beginning of the year.

Americans remain generally pessimistic, the poll found. Only 27 percent say the country is moving in the right direction, while 69 percent say it is on the wrong track, a slight improvement from the October poll.

The poll was based on telephone interviews of 1,102 adults, 443 of them registered Republicans. The margin of error for all adults is plus or minus 3 percentage points; for Republicans the margin of error is plus or minus 4.7 percentage points.