BLACKPOOL, England -- Opposition Labour leader Tony Blair moved his traditionally left-wing party to the center of British politics Tuesday in an unabashed appeal for the middle-class votes he needs to become prime minister.


Making his debut speech as leader to the party's annual conference, Blair dramatically underscored his claim to the political mainstream by saying he would consider repealing a key commitment to nationalization in Labour's constitution.


"Parties that do not change die," Blair said. "This is a modern party living in an age of change. It requires a modern constitution that says what we are in terms the public cannot misunderstand and (Conservatives) cannot misrepresent."


Miners' leader Arthur Scargill, one of the left-wingers fighting to reassert Labour's working-class values, said Blair had declared war on socialism.


But most delegates, sensing power is in Labour's grasp after 15 years in opposition, gave Blair one of the longest standing ovations in years. Labour holds a lead of more than 20 points over the ruling Conservatives in opinion polls.


Blair's promise to draw up a new statement of Labour's objectives was a closely guarded secret -- even his senior colleagues were surprised by it -- and the debate it will open could be a recipe for bitter divisions.


But he said it was a vital step to reach out to voters disenchanted with what he scathingly called Prime Minister John Major's "feckless, irresponsible group of incompetents".


"If the world changes, and we don't, then we become of no use to the world. Our principles cease being principles and just ossify into dogma," Blair told delegates assembled in the northwestern seaside resort of Blackpool.


It was the second time in a week that he had turned the party on its head. Last Tuesday he ditched Labour's traditional image of a tax-and-spend party and promised to work with business and industry to build up a dynamic market economy.


Blair, who has been leader only since July when he succeeded the late John Smith, portrayed Labour as a party voters could trust after 15 years of Conservative "greed and privilege" had undermined British society.


"Today politics is moving to our ground. Across the nation, across class, across political boundaries, the Labour Party is once again able to represent all the British people," said Blair. "We are back as the party of the majority in British politics." He reaffirmed Labour's commitment to a national minimum wage and said he would sign up for social legislation under the Maastricht Treaty of European Union.


But he carefully distanced himself from Labour's left wing by refusing to undertake to repeal the Conservatives' trade union laws and said taxation under a Labour government would be fair.