In the past, Lugar has resisted suggestions that Iraq be divided in three among Kurds, Sunnis, and Shiites.

Biden’s proposal does not go so far as to call for complete autonomy for Kurdish, Sunni, and Shiite regions. Instead, it proposes that the U.S. support a political settlement in Iraq creating a federal system of government and establishing federal regions.

During an impassioned speech on the Senate floor Friday, Biden said he envisioned Baghdad as a shared, neutral city that would not have the power of a national capital to rule over Iraq.  Biden made a direct appeal to Lugar, who sat a few desks away, during his nearly hour-long speech.

Lugar this week noted that Sen. Sam Brownback (Kan.), a conservative running for the Republican presidential nomination, is a cosponsor of the resolution. Republican Sens. Kay Bailey Hutchison (Texas) and Arlen Specter (Pa.) are also cosponsors.

Lugar also pointed out that Biden’s amendment to the Defense authorization bill is a sense of the Congress resolution, and does not have the binding force of law.

Lugar’s support, given his standing as a well-respected centrist on foreign affairs issues, will put more pressure on Biden’s presidential rivals, Sens. Hillary Rodham Clinton (D-N.Y.), Barack Obama (D-Ill.), and Chris Dodd (D-Conn.) to vote for it.

An aide to Lugar predicted “most senators are going to vote for the Biden resolution.”

For Clinton, Obama, and Dodd to oppose it would be to risk appearing out of step with the Democrats and centrist Republicans. Voting for it could give Biden an important political victory.

A spokeswoman for Biden said she was not certain when the Senate would vote on the measure.