Nearly 500 lawmakers -- a third of the 100-seat US Senate and the entire 435-seat House -- are to be sworn in after the November 7 election, which saw heavy losses inflicted on the Republicans, mainly over the Iraq war.

In the House of Representatives, Nancy Pelosi, 66, will become the first female majority leader. Ever smiling and brimming with energy, she has been an implacable Bush opponent.

Holocaust survivor Tom Lantos, 78, who voted for the Iraq war and now is calling for dialogue with Syria and Iran, will head the House Foreign Relations Committee.

In the Senate another fierce White House opponent, Harry Reid, 67, will be the new majority leader, while Joseph Biden, 63, who hopes to run for the White House in 2008, will head the Senate Foreign Relations Committee.

The new Democratic majority has set high on their agenda hearings on quelling sectarian strife in Iraq and perceived administration mistakes getting into the war.

The new Congress will open as Bush prepares to announce an overhaul of his Iraq policy. Key proposals Bush is expected to announce in the next weeks is a short-term "surge" of thousands of additional US troops into Iraq.

The president however will face resistance from Capitol Hill after six years of an overwhelmingly sympathetic Republican-led Congress, and Democrats say he will have to compromise if he hopes to achieve anything substantive in his last two years in office.

"Democrats ran on a message of compromise and we certainly want to work with the president," said Democratic Senator Charles Schumer.

"We hope that when the president says compromise, it means more than 'do it my way,' which is what he's meant in the past," he said.

Indications are the Democrats plan to fully use their newfound clout.

Senate Foreign Relations Committee chairman Joe Biden is organising up to a dozen hearings on the Iraq war, with Secretary of State Condoleezza Rice to testify.

Carl Levin, his counterpart on the Senate Armed Services Committee, plans to summon new Defence Secretary Robert Gates and other officials.

The first dogfight could come over Bush's expected shakeup of Iraq war policy: Biden has already said he would oppose any effort to increase US troop levels.

Even some Republicans in Congress sounded hesitant about a short-term force increase, saying they prefer to defer to military experts -- some of whom also oppose the surge.

"I am reluctant to try to give advice to our military commanders in the field," said Republican Representative Steve King, in a sentiment echoed by several lawmakers.

"I trust their judgment. Every one of them tells me that they are not in a tactical risk of losing this war," he said.

Bush called Wednesday for better collaboration between the administration and the legislature.

"It's time to set aside politics and focus on the future," Bush said after a meeting with members of his cabinet and ahead of a White House reception for Democratic and Republican leaders.

Despite Democrats' new authority in Congress, the president can still veto any legislation he dislikes. Internal Democratic divisions could also be harmful, making some cooperation likely with Republicans.

But some quarters will want Democrats to press the administration hard on the war, as demonstrated by a small protest led by prominent anti-war activist Cindy Sheehan inside the House.

"De-escalate! Investigate! Troops home now!" Sheehan and about a dozen other protesters chanted at Democratic leaders who had assembled for a press conference on their agenda in the House Cannon Office Building.

Sheehan, whose son Casey was killed in Iraq in April 2004, rose to national prominence when she camped outside of Bush's Texas ranch to demonstrate her opposition to the US-led war.