Gordon Brown yesterday finally fulfilled his dream to become Britain’s prime minister after more than a decade of waiting, and he pledged to make a decisive break from the Blair era.

Mr. Brown, after spending almost an hour at Buckingham Palace with Queen Elizabeth — nearly twice as long as the time given to Tony Blair — made a short but stirring speech at Downing Street before entering no. 10 for the first time as leader of the country.

A clearly emotional but nervous Mr. Brown, clutching the hand of his wife, Sarah, finally stepped out from Mr. Blair’s considerable shadow with a promise to heal the divisions within his own party and the country over the Iraq war. He also signaled a new, more low-key style of government in stark contrast to the flamboyance of his predecessor.

“This will be a new government with new priorities,” Mr. Brown declared. “I remember words that have stayed with me since my childhood and which matter a great deal today — my school motto — ‘I will try my utmost.'”

There was conspicuously no mention of Iraq, the issue which dogged the final years of Mr. Blair’s premiership, and he repeatedly emphasized that he could provide the country with the “change” it wanted.

He stressed that his domestic priorities were “change in our NHS, change in our schools, change with affordable housing, change to build trust in Government, change to protect and extend the British way of life.”

Mr. Brown said, “This is my promise to all of the people of Britain and now, let the work of change begin.”

President Bush was the first world leader to telephone to congratulate the new prime minister. President Sarkozy of France invited Mr. Brown to visit Paris in a telephone call late in the afternoon.

In another day of high drama and emotion at Westminster, Mr. Blair was given the rare accolade of a standing ovation from Labor and Opposition Conservative MPs after his farewell performance at the dispatch box watched by his children and his wife, Cherie, from the public gallery.

Mr. Blair paid tribute to the latest British casualties in Iraq and Afghanistan, saying he was “truly sorry” for the dangers faced by Britain’s armed forces. His voice cracked and he appeared to be blinking away tears.

But he again defended his actions over the Iraq war, telling MPs British forces were now fighting “or the security of this country in the wider world against people who would destroy our way of life.”

After Labour MPs rose to their feet Tory MPs looked on, uncertain how to react. Then many reluctantly got to their feet after David Cameron stood up and urged them to join in.

Margaret Beckett, the foreign secretary, who appeared to have lost a rearguard battle to remain as foreign secretary, was in tears as Mr. Blair departed after a vintage performance.

Mr. Blair left the chamber for the last time his career in British politics behind him, to say farewell to his staff before going to Buckingham Palace and then to his Sedgefield constituency to resign as an MP. He quickly experienced the realities of being an ex-prime minister, as he carried his own bag on to the train taking him to his constituency — and then arrived at the other end to find no car was waiting for him.