[jojo07]

DES MOINES, Iowa (Reuters) - Democratic candidates Hillary Clinton and Barack Obama sparred over who has the most experience to be president on Monday as a new poll showed Obama narrowly leading in the crucial kick-off state of Iowa.

The Washington Post-ABC News poll showed Obama with the support of 30 percent of likely Democratic caucus-goers in Iowa, compared to 26 percent for Clinton, 22 percent for former Sen. John Edwards and 11 percent for New Mexico Gov. Bill Richardson.

The poll had a margin of error of plus or minus four percentage points, meaning that Obama's lead was within that statistical uncertainty zone.

Other polls give Clinton a slight edge in Iowa, which on January 3 opens the state-by-state battle to pick the Democratic and Republican contenders in the November 4, 2008, election. The last Washington Post-ABC News poll in Iowa, in late July, showed Obama with a one-point lead over Clinton.

As Americans prepared to celebrate the Thanksgiving holiday on Thursday, Clinton used a campaign speech in Knoxville, Iowa, to try to set herself apart from Obama and Edwards.

Without mentioning the other Democrats by name, Clinton suggested he rivals lacked the experience to take on America's economic challenges, saying "we can't afford on-the-job training for our next president."

"We need a president who understands the magnitude and complexity of the challenges we face, and has the strength and experience to address them from Day One," she said.

Obama dismissed Clinton's comments and questioned Clinton's experience. She was first lady when her husband, Bill Clinton, was president in the 1990s, and has been a New York senator for nearly seven years.

"I am happy to compare my experiences to hers when it comes to the economy. My understanding is that she wasn't treasury secretary in the Clinton administration," Obama said. "I don't know exactly what experiences she's claiming."

Edwards said in a statement Clinton represents the status quo in Washington, not change.

"I believe at the end of the day the American people understand the fundamental differences between the system she has chosen to defend and the change I will bring to America," he said.

At a time when rising gasoline prices and a mortgage loan crisis have rattled markets and raised concerns about a recession, Clinton said Republican presidential candidates would continue Bush's economic policies.

"What is truly amazing ... is that the Republican candidates for president are determined to continue these failed policies. In fact, we can describe their approach to the economy in four simple words: More of the same," she said.

REPUBLICANS FIRE BACK

Republican candidates have directed fire at Clinton daily, hoping to generate enthusiasm among the party faithful. The campaign of a leading Republican candidate, former Massachusetts Gov. Mitt Romney, fired back sharply, saying it is she who lacks the experience to be president.

"Sen. Clinton has shown us time and time again that she is more interested in political posturing than any core principle," said Romney spokesman Kevin Madden.

Danny Diaz, spokesman for the Republican National Committee, said: "Hillary Clinton should finish the debate with herself on key issues confronting the nation before she tries to take on any of the Republican candidates."

Former New York Mayor Rudy Giuliani, leading national polls for his party's presidential nomination but anxious to make up ground on Romney in Iowa and New Hampshire, vowed better control of the porous U.S. border with Mexico on a visit to the border town of McAllen, Texas.

Illegal immigration is a central issue for Republican voters, particularly in Iowa and elsewhere in the Midwest.