LONDON — Treasury chief Gordon Brown today launched his campaign to become Britain's next prime minister and win back voters disenchanted after a decade of Labour Party rule.

Brown said his government would honor Britain's commitments in Iraq but acknowledged mistakes had been made, and he pledged that his government would be more open and cooperate more with Parliament.

"We will keep our obligations to the Iraqi people. These are obligations that are part of U.N. resolution, they are in support of a democracy."

He said he would be talking to Iraqi government officials and British forces in the country.

"I do think that over the next few months the emphasis will shift. We've got to concentrate more on political reconciliation in Iraq. We've got to concentrate more on economic development so that people in Iraq ... feel that they have a stake in the country for the future," Brown said.

Britain ranks second, after the United States, in terms of troops committed to Iraq. The British total is 7,100 but a reduction to 5,000 is planned for later in the year.

President Bush seemed optimistic Thursday about the possibility of continuity on Iraq between Prime Minister Tony Blair and his likely successor.

The president told reporters that he believes Brown "understands the consequences of failure" in Iraq. As Bush sees it, a U.S. defeat would give a boost to terrorism.

Blair, who is stepping down on June 27, formally endorsed Brown shortly before the Treasury chief began a series of appearances today.

"He has a quite extraordinary and rare ability, a tremendous talent to be put at the service of our country," Blair said of Brown, who faces no serious opposition in his bid for promotion.

Often described as dour, the 56-year-old Brown has been accused of "Stalinist ruthlessness" and a lack of people skills.

The general elections will pit Brown, a rumpled intellect, against David Cameron, the fresh-faced Conservative Party leader who has been compared to the younger charismatic Blair.

Brown has close ties to the U.S. Democratic Party, and was said to have been particularly close to Massachusetts Sen. John Kerry. President Bush said Brown was "an open and engaging person."

"And I found him to be an easy-to-talk-to, good thinker," Bush said Thursday.