LONDON, Sept. 11 — In his first major foreign policy address, David Cameron, the leader of Britain’s opposition Conservatives, sought today to distance his party from what he called a “slavish” bond between Britain and the United States established by Tony Blair.

As he spoke, Mr. Cameron asked a well-heeled audience of several hundred bankers and policy experts in London’s financial district to bow their heads in silence at the precise moment when the first hijacked plane slammed into the World Trade Center on Sept. 11, 2001.

Mr. Cameron is the main opposition contender likely to challenge whoever takes over the ruling Labor Party from Mr. Blair, who has promised to quit within a year. Mr. Cameron’s remarks were designed partly to demarcate his foreign policy sharply from that of Mr. Blair, for whom the war in Iraq and the association with President Bush has proved politically damaging.

The speech was also intended to draw a line under previous Conservative policy. Mr. Cameron himself supported the Iraq invasion in 2003, but, said a senior Conservative who requested anonymity under party rules, “we don’t want to have an endless fight about what happened three or four years ago. This is about the next 10 years.”