Presidential candidate Bill Richardson is accusing his Democratic rivals in the Senate of creating too many escape clauses for President Bush to leave U.S. troops in Iraq indefinitely.

In a speech planned Tuesday before liberal activists, the New Mexico governor tried to differentiate himself in the primary race by stressing that he would leave "zero troops" in Iraq. He pointed out that his leading opponents have supported legislation that would leave behind an undetermined number of residual forces to train and equip Iraqi forces, among other things.

"With all due respect to my Democratic colleagues, Senators Clinton, Obama, Dodd and Biden all voted for timeline legislation that had deliberate loopholes," Richardson said in prepared remarks. "Those loopholes allow this president, or any president, to leave an undetermined number of troops in Iraq indefinitely. And this is the same legislation that former Senator Edwards says we should send back to President Bush over and over again until he signs it."

Richardson would leave a small Marine contingent behind in Iraq to protect the U.S. Embassy. But, he said, "if the embassy isn't safe, they're coming home too, along with embassy personnel."

He was among several candidates expected to address the conference organized by the Campaign For America's Future, a gathering of more than 3,000 progressive activists who are overwhelmingly opposed to the war. A year ago, New York Sen. Hillary Rodham Clinton was booed at the conference for opposing a set date for pulling U.S. troops from Iraq.

Former North Carolina Sen. John Edwards and Illinois Sen. Barack Obama were scheduled to speak midday Tuesday. Clinton and Ohio Rep. Dennis Kucinich were scheduled to speak Wednesday.

Until now, Richardson has typically been less critical of his opponents, repeatedly saying that the important thing is to elect a Democrat in 2008 and proposing that the candidates sign a pledge against going negative against each other.

Richardson's new approach comes as he is moving up in polls in the early voting states of Iowa and New Hampshire, thanks to a successful television ad campaign. He still trails Clinton, Edwards and Obama in those states and is even farther behind nationally.