In his speech to British lawmakers, the president will attempt to erase what he believes are misconceptions about America's use of force. Aides to the president say he will subtly invoke Europe's history of appeasement of dictators, and the price Europeans paid in those days for their governments' inaction.
Mr. Bush is also expected to explicitly remind Europeans about the critical work the Allies did to set postwar Germany on the path to democracy, a process the Bush administration and the British are trying to accelerate today in Iraq.
Earlier, Queen Elizabeth II and Prince Philip gave a royal salute to the American leader, greeting Mr. Bush at Buckingham Palace.
As ceremonial cannon blasts from a 41-gun salute shook the palace, Bush and his wife, Laura, moved down a receiving line with the queen and prince, greeting Blair, Foreign Secretary Jack Straw and a phalanx of military officers in formal dress.
A security cordon of thousands of police officers and hundreds of American Secret Servicemen was unable to prevent an embarrassing security snafu at the palace.
A reporter for London's Daily Mirror says he had no trouble using a phony reference to get a job as a palace servant - and had he wanted to kill the Queen or Mr. Bush, it would have been easy to do.
A spokeswoman for the palace says a "full investigation" is being done into how Parry pulled off his masquerade.
Security costs for the Bush visit are now estimated at approaching $9 million, with over a thousand police officers on patrol, some of them armed with guns - unusual in Britain - as well as batons and pepper spray.
Anti-Bush protesters are planning a few small rallies Tuesday, including one outside the heavily guarded U.S. Embassy, in support of al Qaeda and Taliban terrorist suspects detained without trial in Guantanamo Bay, Cuba.
The real test of anti-Bush sentiment comes Thursday. The Stop the War Coalition expects 100,000 to march past Parliament and Blair's nearby Downing Street office.
Fewer than 100 anti-war protesters were standing outside Buckingham Palace on Tuesday night as the Bush entourage arrived in two helicopters. The president and wife Laura landed deep inside the walled-off estate in central London, far beyond earshot of a few dozen stalwarts shouting "Bush go home!" and other invectives.
"I think he (Bush) is a disgrace," said one demonstrator. "I think he is a disgrace to the American people and these demonstrations are in solidarity with the American people. We are not anti-American - we are anti-Bush."
A few in the crowd outside the palace wanted Mr. Bush to know they back him to the hilt.
"I support my president. He's facing a tough crowd over here," said Mike Rigas, 31, a Boston native working in a bank in London. Rigas said most Britons he talked to were fairly supportive of the president.
Mr. Bush argues that all free countries are at risk from terrorism, and that Iraq is a central front in the battle against terrorists. Wednesday, he was broadening his argument by offering what his senior aides called a "three-pillared" argument for war as a last resort.
Mr. Bush was noting Europe's long history of wars, which in the White House view has created the Europeans' tendency to embrace international cooperative organizations like the United Nations.
The president was saying that he too respected such groupings, so long as they are "strong, international institutions and alliances that are effective." He was praising the spread of democracy, while saying that "history has shown that there are times when countries must use force to defend the peace and to defend values."
Mr. Bush did not plan to define which values he was referring to, nor when, exactly, war is necessary.
Also Wednesday, Mr. Bush was to meet with relatives of British victims of the Sept. 11 attacks and British veterans of the war in Iraq. Britain has sent more troops to Iraq than any country aside from America, about 9,000, and the British have lost more than any other American ally — 52 deaths since the start of the war.
Later on the Bush schedule: a banquet at the palace with the queen, Blair and numerous dignitaries.
Mr. Bush's visit to Britain dominated broadsheet newspapers in the country Wednesday morning. Headlines concentrated on the unprecedented level of security surrounding the visit, with The Times of London's front page leading with "President strolls into Fortress Britain."
Iraq is not the only division between many Britons and the president. Earlier Tuesday, more than 500 environmentalists paraded to the U.S. Embassy to protest Mr. Bush's 2001 rejection of the Kyoto treaty, which proposed tough new pollution-eradication standards that the president called unrealistic.
Some British officials — Blair included — were angered by Mr. Bush's decision last year to slap tariffs on imported steel, duties that the World Trade Organization has declared illegal.
Mr. Bush is close to deciding whether to repeal the tariffs, but senior administration officials said Mr. Bush would make no promises to Blair on Tuesday.