U.S. presidential contenders have embarked on a rigorous schedule of campaign events that will lead up to the beginning of the 2008 election process in January.  VOA national correspondent Jim Malone reports from Washington.

The Labor Day holiday marks the traditional end of summer in the United States.  But this year it also marks the beginning of an intense period in the 2008 presidential election process.

Several contenders from both major political parties fanned out across the early contest states of Iowa and New Hampshire, including the frontrunner for the Democratic Party's presidential nomination, Senator Hillary Clinton of New York.

Sen. Hillary Rodham Clinton speaks to Alliance for Retired Americans 2007 Legislative Conference in Washington, 04 Sept 2007

Clinton faces a strong challenge from Illinois Senator Barack Obama and former North Carolina Senator John Edwards, who picked up endorsements from labor unions representing steelworkers and coal miners.

Obama took his campaign to New Hampshire, which is expected to hold the nation's first presidential primary in January.

"I might not have the experience Washington likes, but I believe I have the experience America needs right now." he said.

Several Republican presidential hopefuls were busy on the campaign trail as well, including former Massachusetts Governor Mitt Romney.

Romney leads in the early contest states of Iowa and New Hampshire, but trails in national polls behind former New York City Mayor Rudy Giuliani and former Tennessee Senator Fred Thompson.

The Romney campaign is airing a new television ad that shows the candidate jogging, an apparent attempt to highlight the fact that Romney is younger that most of the other major Republican contenders.

Mitt Romney at a Labor Day parade in Milford, New Hampshire, 03 Sept 2007

Thompson is scheduled to officially enter the race for the Republican presidential nomination on Thursday.

Political analysts expect Iraq will be the top issue in next year's presidential campaign.

"Iraq is the big issue," said John Fortier, an expert at the American Enterprise Institute in Washington. "It is one that is weighing down the president and really putting Republicans in a difficult position because most Republicans are somewhat supportive of the war whereas certainly most Democrats, but also most independents, are really, really worried about the war and really have turned against the president and his strategy."

The actual nomination process for both parties is expected to get underway in January.  But several states are attempting to move up the date of their primaries, forcing traditional early contest states like Iowa, New Hampshire, and South Carolina to consider holding their caucuses and primaries earlier than ever.