In a blizzard of appearances on political talk shows, National Security Adviser Stephen Hadley said the administration took the intervention of Senators John Warner and Richard Lugar seriously.

But the Republican elders should wait for a mid-September report by General David Petraeus, the US commander in Iraq, before revisiting their proposal for planning to start on a phased withdrawal of US forces.

"And the opening shot really ought to be to hear from the commanders on the ground who can make an assessment of where we are in our strategy," he said on ABC television.

But Warner, an armed services expert, signalled that patience in Congress with President George W Bush's strategy was wearing thin.

Asked if the current Iraq mission would pass if it were put up for a vote today, Warner said: "I doubt very much that it would."

Warner and Lugar, one of the top Republican voices on foreign policy, Friday introduced a bid to force Bush to change course and curtail his "surge" of nearly 30,000 extra troops into Iraq.

They proposed that Congress should reauthorise a sharply narrowed US mission in Iraq, to pull troops out of the sectarian cross-fire and retool them to battle extremists, train Iraqi soldiers and secure Iraq's borders.