WASHINGTON – U.S. Democratic presidential hopefuls flexed their muscles this Labor Day weekend as they geared up for a grueling primary election season that will help determine the candidate who will face off with President George W. Bush in November 2004. "This campaign will really begin to heat up after Labor Day," said Iowa Democratic Governor Tom Vilsack. "This thing is just getting started."

In coming weeks, the nine Democratic candidates vying for the White House will have to produce a frontrunner able to challenge President Bush, who currently is leading in opinion polls.

But before taking on the president, the Democrats will have to distinguish themselves in a series of four public debates, start running television advertisements and raise as much money as they can.

However, 15 months before the 2004 election, none of the Democratic contenders appears able to take on Bush, despite the fact that the president has to cope with what increasingly appears like a quagmire in Iraq and the fragile U.S. economy, AFP reported.

As a result, two-thirds of U.S. voters were incapable of naming the Democratic candidates, according to the latest CBS News opinion poll.

The most unexpected rival for President Bush would be Howard Dean, 55, who was unknown to many Democrats and the public at large only three months ago. The former Vermont governor and physician, who is a fierce opponent of the war in Iraq, is leading in opinion surveys in Iowa, which will hold a straw poll on January 19, and New Hampshire where Democrats will hold a primary on January 27.

Dean also led his rivals in fundraising in the second quarter of the year, having collected 7.5 million dollars, mostly on the Internet.

In opinion polls, he is leading Senators John Kerry of Massachusetts, John Edwards of North Carolina and Joseph Lieberman of Connecticut as well as Representative Richard Gephardt of Missouri.

The remaining Democratic candidates such as Al Sharpton, Florida Senator Bob Graham, Congressman Dennis Kucinich of Ohio and former senator Carol Moseley Braun. "He's got the energy, the excitement," Joe Andrew, a former head of the Democratic National Committee, said of Dean. "He's got the large committed group of people getting involved in politics for the first time. These are all the conditions that Bill Clinton had in 1992."

The Democratic field of candidates may even grow as former supreme NATO commander retired general Wesley Clark could decide in the next few days to enter the battle for the presidential nomination.

Fifty-eight-year-old Clark, who is close to Clinton, is held in high regard because of his role in leading the Western alliance against Serbian forces in Kosovo in 1999.

A late entry into the race does not necessarily put a candidate at a disadvantage.

The newspaper ***USA Today*** noted last week that early leaders in the Democratic nomination race have sometimes failed to win the prize.

That happened to Edward Kennedy in 1979, Gary Hart in 1987 and Mario Ciomo in 1991, who all failed to become their party's presidential nominees.