CNN

Richardson criticized his Democratic rivals Tuesday over Iraq.

WASHINGTON (CNN) - Even as he praised the 2008 Democratic field to a gathering of progressive activists, New Mexico Gov. Bill Richardson offered a polite but tough point-by-point critique of his fellow competitors' approach to ending the Iraq war.

"With all due respect to my Democratic colleagues, Senators Clinton, Obama, Dodd and Biden all voted for timeline legislation that had deliberate loopholes," he told the "Take Back America" conference in Washington. "This is the same legislation that former Senator John Edwards says we should send back to President Bush over and over again until he signs it."

Richardson said his "new worldview" involves a plan for Iraq that would call for all troops to be withdrawn by the end of the calendar year with no residual troops to be left in Iraq performing security duties or manning airbases.

Richardson, citing a press report, said Sen. Clinton "told her military advisor that if she were elected, there still might be troops in Iraq at the end of her second term."

The New Mexico governor has increased his standing in the polls in some early states, but acknowledged he needs to lay out the differences between him and his opponents in order to break through.

"I'm not being negative," he said later at a press conference. "I am pointing out differences."

READ MORE behind-the-scenes coverage on whether the military thinks the troop surge in Iraq is working.

- CNN Senior Political Producer Sasha Johnson