Representative John Murtha, who chairs the House Subcommittee on Defence and is close to House Speaker Nancy Pelosi, made the comment Sunday in response to repeated threats by the president to veto legislation that calls for withdrawal of US troops from Iraq by the end of next March.

"There's three ways or four ways to influence a president," Murtha said on CBS's "Face the Nation" programme. "One is popular opinion, the election, third is impeachment and fourth is the purse."

Asked specifically if Democrats, who now control the US Congress, were seriously contemplating the impeachment option, the congressman responded: "What I'm saying, there's four ways to influence a president ... And one of them's impeachment."

Some of the fiercest critics of President Bush have long charged he has illegally manipulated intelligence to accuse the Iraqi government of late president Saddam Hussein of secretly stockpiling weapons of mass destruction, thereby creating a pretext for the March 2003 invasion of Iraq.

No weapons of mass destruction have been found in Iraq since the invasion but the White House has strongly denied the intelligence manipulation charge.

The impeachment threat is being dangled as the White House and congressional Democrats face a new showdown over Iraq policy in coming weeks.

A 124-billion-dollar war funding bill passed by the House of Representatives Wednesday and the Senate on Thursday established a non-binding target of completing a US combat troop pullout from Iraq by March 31, 2008.

The measure is expected to land on the president's desk on Tuesday, the fourth anniversary of his now much ridiculed "Mission Accomplished" speech, in which he, standing on the deck of an aircraft carrier off the coast of California, declared an end to major combat operations in Iraq.

As promised, Bush will wield his veto pen, and Democrats acknowledge they lack the votes to override his decision.

But they have made it clear that while the withdrawal deadline will most likely be dropped, they still would like to come up with a bill that would place limits and conditions on future US operations in Iraq.

One of the proposals, according to Murtha, calls for making the continued US military presence in Iraq contingent on the Iraqi government meeting specific political benchmarks designed to stem violence.

They include showing progress in reaching power-sharing arrangement that would bolster the role of Sunnis in the Iraqi government, an agreement to equitable distribution of oil wealth, and a crackdown on militias.

Murtha also suggested limiting the life of a revised war-funding bill from one year to just two months to allow for an earlier congressional review of the situation.