WASHINGTON - US President Bush will tell the nation Wednesday night he will send more than 20,000 additional American forces to Iraq, acknowledging that it had been a mistake earlier not to have more American and Iraqi troops fighting the war, a senior administration official said.

President Bush meets with European Commission President Jose Manuel Barroso, not shown, in the Oval Office of the White House in Washington, Monday, Jan. 8, 2007. [AP]

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Seeking support for a retooled strategy to win support for the unpopular war, the president also will acknowledge that the rules of engagement were flawed, White House counselor Dan Bartlett said.

Even before Bush's speaks, Democrats were laying plans to register their opposition to the troop buildup. House Speaker Nancy Pelosi pledged to hold a vote on the increase, trying to isolate Bush on his handling of the war. In the Senate, Democrat Edward M. Kennedy has sponsored legislation to require Bush to get congressional approval before sending more troops to Iraq.

For a little over 20 minutes Wednesday night, Bush is to explain why a gradual buildup of about 20,000 additional US troops, along with other steps expected to include pumping $1 billion into Iraq's economy, is the answer for a more than 31/2-year-old war that has only gotten deadlier with no end in sight.

Bartlett did a round of interviews on television morning shows to set the stage for the president's address.

"A vast majority of the American people are not satisfied with the progress in Iraq," Bartlett said. "President Bush is in their camp. He's not satisfied, he's going to say the strategy was not working, he's going to tell them specifically how we're going to fix the strategy."

Bush will say that the infusion of additional American forces will depend on Iraq taking specific steps to curb sectarian violence and make other moves to deal with political and economic problems. The first batch of new US troops is expected to be in Iraq within three weeks.

Bartlett also said that Bush will "make very clear that America's commitment is not open-ended, that benchmarks have to be met, that milestones have to be reached both on the security side but just as importantly on the political side and the economic side. It will be unequivocal in President Bush's speech tonight that the Iraqis have to step up."

In his speech, Bush was to acknowledge that mistakes have been made, Bartlett said.

"The president will say very clearly tonight that there were mistakes with the earlier operations, that it did not have enough Iraqi troops or US troops, that the rules of engagement - the terms in which our troops would actually conduct these operations - were flawed," Bartlett said.

After nearly four years of fighting, $400 billion and thousands of American and Iraqi lives lost, the White House calls the president's prime-time address from the White House library just the start of a debate over Iraq's many problems.

The address - one of the most pivotal of Bush's presidency - is the centerpiece of an aggressive public relations campaign that also will include detailed briefings for lawmakers and reporters, trips abroad by Cabinet members and a series of appearances by Bush starting with a trip Thursday to Fort Benning, Ga.

Since Friday, Bush has briefed about 100 lawmakers - meetings that were to culminate Wednesday with Congress' Democratic leadership and their Republican counterparts.

Bush on Tuesday also talked by telephone with key foreign allies. He filled in the leaders of Britain, Australia and Denmark, with more calls planned.

Crafting the new policy took the president nearly three months. Relevant agencies conducted reviews, outside experts were called in, and the president consulted several times with Iraqi Prime Minister Nouri al-Maliki and other prominent Iraqi leaders.

In the meantime, the sectarian violence in Iraq continued unabated, and public approval of Bush's handling of the Iraq war hit a record low of 27 percent in December, according to an AP-Ipsos poll.

The president will say that the 132,000 troops now in Iraq will be augmented with more sent to both Baghdad, which has been consumed by sectarian violence, and the western Anbar Province, a base of the Sunni insurgency and foreign al-Qaida fighters.

Moving first into Iraq will be the 2nd Brigade, 82nd Airborne Division, which is now in Kuwait and poised to head quickly into the country, the defense official said. The brigade, numbering about 3,500 troops, is based at Fort Bragg, N.C.

Bush is expected to link increases in both US troops and economic aid to moves by the Shiite-led Iraqi government to bridge sectarian divisions. Those include taking steps to curb Shiite militias, enacting a plan to distribute oil revenue to all the country's sects and easing government restrictions on deposed leader Saddam Hussein's Baath Party.

The Baghdad government also will be required to commit more money toward reconstruction and more troops into the fight.

Other components of the president's plan include a bit over $1 billion to shore up Iraq's battered economy and create jobs and a call for friendly Mideast countries - some of which Secretary of State Condoleezza Rice is visiting starting Friday - to increase their aid to Iraq, said a second official, who also requested anonymity.

The president will ignore the recommendation of the bipartisan Iraq Study Group that he include Syria and Iran in an effort to staunch Iraqi bloodshed, the official said.