British Prime Minister Tony Blair is leaving London today to begin a four-nation tour of west Africa.

His first stop is Nigeria, a former British colony that has moved from military to civilian rule, though tribal conflicts continue.

Mr. Blair will also visit Ghana, Sierra Leone and Senegal.

The prime minister hopes his trip will lead to more support for Africa from the world's industrial powers.

In an interview published before his departure Wednesday, Mr. Blair said the international community has what he called "the best chance in a generation" to help Africa defeat poverty, disease and war.

He said the West has a duty to act in Africa, or run the risk of seeing the emergence of more failed states, like Afghanistan, where terrorism and drug production can proliferate.

Britain's international development secretary, Clare Short, is accompanying Mr. Blair. In an interview on British television, she dismissed domestic critics who say Mr. Blair should concentrate on problems at home instead of trying to rescue Africa.

"Surely most decent people believe that politics is about trying to make the world most just and more decent. Africa is crying out for a better chance for its people," she said.

Britain wants the world's eight leading industrial powers to agree at a summit in June in Canada to implement what is called the New Partnership for African Development.

The plan proposes more trade and financial assistance for African countries, in exchange for democratic and economic reforms, and respect for human rights.