Romney's unique investment in the state appears to be paying off, with the help of the big dive Rudy Giuliani's numbers have taken after poor showings in previous states.

Romney leads John McCain by 15 points, 34 percent to 19 percent. Giuliani, who led the last Review-Journal poll, is in sixth place.

Democrats and Republicans hold presidential nominating caucuses in Nevada on Saturday, at 11 a.m. and 9 a.m. respectively.

The poll of 500 likely caucus-goers for each party was conducted by Mason-Dixon Polling & Research Inc. from Monday through Wednesday and carries a margin of error of plus or minus 4.5 percentage points.

"Clinton's base is women and voters over 50, and she does well with Hispanic voters," said pollster Brad Coker, Mason-Dixon managing partner. "Those have been the national patterns, and Nevada, I think, is more reflective of the nation as a whole than either Iowa or New Hampshire."

Obama dominates among black voters, favored by 65 percent to Clinton's 18 percent, but they make up just 10 percent of likely caucus-goers. Hispanics make up 15 percent of likely caucus-goers and favor Clinton over Obama by 50 percent to 29 percent.

Obama, who has gotten a major boost from the Culinary union, also leads among union households, but by only 7 percentage points over Clinton. Edwards, despite his focus on the labor vote, is in third place in this and almost every other group.

As for Romney, Coker noted that he is Republican caucus-goers' favorite candidate on every issue and across every voter group except those describing themselves as born-again Christians, who favored Mike Huckabee.

"In every other state we've polled, the issues are split. Huckabee wins on moral values, McCain wins on the war on terror, immigration is split, taxes are split. Romney does a little bit better on economic issues," Coker said. "Here, Romney is across the board the best on all five issues. I haven't seen that anywhere else, and it tells me he's pretty strong."

Alone among Republicans, Romney has built a significant campaign infrastructure in Nevada, and is completing a two-day swing through the state today.

"He's paid the most attention to the state, he has the organization, and he has national credibility" from second-place finishes in Iowa and New Hampshire. Coker said Romney's lead was the same before and after his win Tuesday in Michigan.

Nevada's Republican caucus is likely to be overshadowed by Saturday's South Carolina Republican primary. A Mason-Dixon poll in South Carolina finds McCain and Huckabee battling for first and Romney and Fred Thompson duking it out for third.

South Carolina Democrats don't vote for another week. Mason-Dixon found a 9-point Obama lead over Clinton there.

Pollsters have come in for criticism since the majority got New Hampshire wildly wrong, predicting an Obama win by double digits when in the end Clinton came away with a narrow victory.

Concerns also have been raised about the difficulty of polling for Nevada's first-time early caucus, since it is difficult to determine who will attend.

Saturday's meetings require in-person, on-time participation in a confusing process Nevadans have not tried before.

"It certainly presents some interesting challenges, but I don't think it's impossible to do," Coker said of polling Nevada. "It took a lot of work, but I think I figured it out. I'm pretty comfortable with the way we did it."

Coker pointed to his track record both here and elsewhere. He noted that Mason-Dixon's final New Hampshire poll was much closer than most -- it had Obama ahead by just 2 points, within the margin of error.

Mason-Dixon had the most accurate prediction of the results of Tuesday's Republican primary in Michigan, predicting an 8-point Romney victory; Romney won by 9 points.

Mason-Dixon has been polling for the Review-Journal in Nevada since the early 1990s, with a good record of accuracy in predicting election results.

Coker said the poll was constructed to capture only those who appeared prepared to actually attend the caucus, and weed out those who didn't realize what it required.

"The screening questions were really designed to bring home the fact that these things are being held at certain times," he said. "If people said they were going to go, we gave them every opportunity to back out. Half of the equation is that the respondent understands" what a caucus requires.

Finding 500 likely Republican caucus-goers took poll-takers more time than finding an adequate number of Democrats, Coker said, signaling that Republican turnout will be low.

The Review-Journal last polled the state about a month ago and found Clinton in the lead by 8 points. In the new poll, Clinton leads among women, 49 percent to 28 percent, and among those 50 and over, 46 percent to 27 percent.

Obama leads among men, 37 percent to 30 percent, and voters under 50, 39 percent to 34 percent. He does better in Clark County, where he polls 34 percent to Clinton's 39 percent, but she leads him by 17 points in Washoe County and 16 points in rural Nevada.

"Hillary Clinton has a solid base of traditional Democrats," said University of Nevada, Reno, political scientist Eric Herzik. "She has the baby boomers. There's a generational split really emerging in this election."

Herzik noted that Clinton had leads of more than 20 points in early polling and has worked hard to bring Nevada Democratic power brokers to her side.

"The story is if she loses," he said. "If she loses Nevada, it's not just a loss, it's a collapse."

Democratic caucus-goers said the quality they most wanted in a candidate was someone who "cares about the issues I care about." Thirty-two percent said that was the most important characteristic, compared to 20 percent looking for a candidate who "represents change and a new approach."

Among those citing experience as their top quality, 84 percent chose Clinton, who had just 10 percent of voters looking for change. Obama was favored by 62 percent of change-seekers, Edwards by 21 percent.

Obama also won with those seeking honesty, 47 percent to Clinton's 26 percent, but Clinton was the favorite of issues voters, 39 percent to Obama's 28 percent.

Democratic voters' top issue was the economy and jobs, with Iraq second, followed by health care. Clinton narrowly beat Obama among voters who said Iraq was their top issue, but dominated with those citing the economy and health care, getting over 50 percent of those surveyed who prioritized those issues.

"I'm surprised she's even close on Iraq," Herzik said. "That's supposed to be Obama's real strength. I couldn't even tell you her position."

Clinton is helped by the fact that economic concerns are eclipsing the war in voters' minds, Herzik said.

On the Republican side, the Review-Journal's December poll had Giuliani in the lead by five points over Romney. In the new poll, Giuliani, who fared miserably in Iowa, New Hampshire and Michigan, has lost Republicans' confidence and is in a single-digit virtual tie with Fred Thompson and Ron Paul.

"The worst news for any candidate here is Giuliani," Herzik said, noting the former New York mayor isn't expecting a strong showing in Saturday's South Carolina primary either.

"He's playing a strategy that really has to come together in Florida on January 29, but it's looking worse and worse for him," Herzik said.

Forty-two percent of Republican voters were looking for a candidate who "shares my values and views on the issues," while 37 percent wanted someone who "has the strength and leadership to keep America safe."

Romney was favored by voters looking for values by 38 percent to Huckabee's 17 percent and McCain's 15 percent. Romney also was the favorite among those who cited leadership, 32 percent to McCain's 20 percent, with Giuliani scoring 13 percent for third.

Republicans' top issue was a three-way tie between national security, the economy and immigration. Romney scored best with voters who cited each of those as well as with those whose top concerns were moral issues and taxes.

"That's very good news for Romney, because ultimately the winner on the Republican side has to be able to bridge the multiple ideological divisions within the party," Herzik said. "So far, no one's been able to do that."

Romney, he noted, probably polls better among Christian conservatives here than elsewhere because of Nevada's relatively large Mormon population.

But Herzik said nobody should crown a winner based on polls before the caucus results come in.

"It's hard enough to get a reliable poll in such a fluid situation, and it's even harder when you're trying to discern caucus-goers," he said. "Buyer beware."

Contact reporter Molly Ball at mball@reviewjournal.com or (702) 387-2919.