Richard Lugar, the most senior Republican yet to break ranks with President George W. Bush over the war, said Bush should embrace moderates from both sides in Congress to chart a new strategy focused on diplomacy.

Lugar, the top Republican on the Senate Foreign Relations Committee, sent shock waves through Washington last week by arguing that US policy in Iraq "has lost contact" with national security interests in the Middle East and beyond.

Speaking on CBS News, the respected 75-year-old fleshed out his dissenting views by calling for a diplomatic forum to bring together the United States, Iraq and all of its neighbouring countries.

He also recommended that a smaller contingent of US troops remain to train Iraqi security forces and secure its borders.

"And then, withdrawal of a majority of American troops in a calm, orderly way, over the next few months, so that we refurbish our ability to meet problems elsewhere in the world," the senator said.

From the floor of the Senate on Monday, Lugar shook the White House by arguing that Bush's "surge" of nearly 30,000 troops had "very limited" chances of success given the pressing timeframe and the political climate in Iraq.

The rising death toll for US personnel in Iraq, and anger over Iraqi authorities' failure to use the surge to seize the political initiative, are stoking Republican discontent.

Lugar, while opposing any Democratic-sponsored cut in war funding, said Bush would be unwise to insist on no change of course as national elections loom next year.

Asked how Republicans would respond to Bush digging in his heels, he said: "Well, many will support that, but not very many."