President Bush will defend his Iraq policy Wednesday in a speech that will be broadcast to the British people. Mr. Bush will tell them that sometimes the use of force is necessary to counter threats to peace and security. With anti-war demonstrators gathering in the streets of London, the president will explain why he chose to use force to oust Iraqi leader Saddam Hussein.

A senior White House official indicates he will address the issue in general, philosophical terms. This official says the president will say that sometimes the use of force is necessary when diplomacy and other means fail.

Mr. Bush will also use the occasion to talk about the importance of nations working together to tackle problems and promote democracy. And he will begin and end the speech with comments about the special ties between the United States and Britain.

The president will deliver the address to an invited audience in London rather than to the British parliament. The speech comes on the first full day of his state visit to Great Britain -- a visit that was scheduled months before the invasion of Iraq.