Forget the pleasantries. The criticism grows sharper by the day in the race for the Republican presidential nomination. The reason: Rudy Giuliani, Mitt Romney, John McCain and Fred Thompson are bunched at the top and trying to emerge with voting to begin in just a matter of weeks. "We're now into a 90-day sprint and each of the campaigns is struggling for a strategy," said Scott Reed, Republican Bob Dole's 1996 campaign manager. "Who do they take out, who do they go after and who do they risk alienating by being the aggressor? They're all trying to figure that out."

There's obvious risk.

Howard Dean and Dick Gephardt went negative in the 2004 Democratic primary, and their strategies backfired. They lost when voters gravitated toward above-the-fray candidates John Kerry and John Edwards.

Four years later, the leading Republican candidates - Thompson, Giuliani, Romney and McCain - are keenly aware that criticizing one another could turn off a certain GOP segment and boost their own negative images in voters' minds.

But given the current circumstances, all of them, to varying degrees, figure the risk is worth the potential benefit - breaking out of the pack to become the clear front-runner.

So, they are taking on one another with increased frequency and heightened ferocity. Thus far, the criticism largely has been limited to rhetoric. Some candidates have poked at their rivals in a handful of radio commercials, but the contrasts have been subtle. None has run negative television ads. Yet.

On Monday, Thompson, the former Tennessee senator, became the latest candidate to criticize. Without naming Giuliani, Thompson suggested the ex-mayor of New York, a one-time Democrat who backs abortion rights and gay rights, was a closet Democrat.

"Some think the way to beat the Democrats in November is to be more like them. I could not disagree more," Thompson said in a speech he was to deliver to the Conservative Party of New York. "I believe that conservatives beat liberals only when we challenge their outdated positions, not embrace them."

Giuliani, in turn, had a former deputy mayor prod Thompson, who has no executive experience and a thin list of Senate accomplishments.

Said Randy Mastro: "Some candidates talk the talk about Republican principles. Others actually have a proven track record of governing according to Republican principles."

Mindful of the possible pitfalls of going negative, Giuliani says he has tried to stick to what he calls Ronald Reagan's 11th commandment of refraining from criticizing a member of his own party. Typically, he assails his GOP opponents only after they go after him. To keep that clean appearance, he sometimes dispatches aides and surrogates to do the dirty work.

National polls show Giuliani maintaining his lead but Thompson giving him a chase. A state-by-state look shows Romney leading in early voting Iowa, while races in other important states like New Hampshire, Michigan and South Carolina are toss-ups.

Explaining the negativity, Whit Ayres, a Republican pollster, said: "It's still anybody's ball game at this point."

"They all are trying to draw distinctions when there are relatively few policy differences among them on the main issues of the day" - Iraq and terrorism among them, he said. Thus, Ayres said, the candidates are focused on other areas like leadership, backgrounds, character and history.

The tit-for-tat over the past week included:

_McCain, the Arizona senator looking to continue gaining ground in New Hampshire and curtail Romney's standing there, took issue with Romney's remark that "I do speak for the Republican wing of the Republican Party." McCain recalled Romney's past support for Democratic candidates and moderate politics in Massachusetts, saying, "Being a Republican wasn't much of a priority for him." Thompson got in the act with an aide issuing a statement critical of Romney.

_Romney and Giuliani squabbled over taxes and spending during a debate in Michigan. Romney criticized Giuliani for challenging a law that gave President Clinton the right to veto spending items line by line. Giuliani said spending fell in New York while he was mayor and rose in Massachusetts while Romney was governor. Later, McCain argued that neither was innocent of raising taxes, and he, too criticized Giuliani on the line-item veto challenge.

_Giuliani, through surrogates and aides, accused Romney of having a lawyers test for going to war, based on a comment the former Massachusetts governor made during the debate. In turn, Romney countered: "If there's somebody that wants to talk about suing and lawyering, the mayor gets first place." He rattled off a host of lawsuits Giuliani filed during his two terms as New York mayor.

More contrasts are likely this week. The Republican hopefuls gather in Washington to speak at events hosted by four influential party or GOP-aligned groups.

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EDITOR'S NOTE - Liz Sidoti covers presidential politics for the Associated Press.