Opening a seven-day, four-nation trip, Mr. Bush warned that Europe may be terrorists' next target.
"Even though we've had some initial successes, there's still danger for countries which embrace freedom, countries such as ours, or Germany, France, Russia or Italy," the president said as he left the White House shortly after dawn.
Hours later, Mr. Bush stepped off Air Force One onto a red carpet lined by white-jacketed military troops. For his only appointment on the first evening of this trip, Mr. Bush ducked into a coffee house at the site of the old Berlin Wall with German Chancellor Gerhard Schroeder, U.S. Ambassador Dan Coats and Berlin Mayor Klaus Wowereit.
He shook hands in the cafe and received a polite round of applause from the selected group drinking coffee and beer.
Previewing the speech he will give the German Parliament on Thursday, Mr. Bush said before leaving Washington, "As an alliance, we must continue to fight against global terror. We've got to be tough."
The blunt words, aimed for consumption at home as well as in Europe, dovetailed with the administration's effort in recent days to prepare Americans for the inevitability of another attack.
Those warnings have been in part a response to Democratic suggestions that the administration missed warning signs before the Sept. 11 attacks, U.S. officials have said.
Mr. Bush is trying to build a case at home and abroad for widening the war beyond Afghanistan to other terrorist hot spots, primarily Iraq. Secretary of State Colin Powell said the president won't shy from that policy in talks with Schroeder.
"They will talk about those nations that are developing weapons of mass destruction that threaten us all and I'm quite confident they'll have a conversation about Iraq in that category," he said.
Almost a picnic atmosphere prevailed here as tens of thousands of people marched in opposition to Mr. Bush's anti-terror war plans, their placards carrying both harsh and humorous messages. "War is terror — stop the global Bush fire," read one.
Another poked fun at Mr. Bush's choking incident: "Pretzels not bombs."
With 10,000 officers, the largest police operation since World War II, officials blocked off several streets around the downtown hotel where Mr. Bush was staying. The hotel is just east of the Brandenburg Gate, the symbolic dividing line between the old communist regime and the West.
A huge portrait of the White House hung from the landmark.
Mr. Bush intended to spend barely 20 hours in the German capital before flying Thursday to Moscow, where he will sign a landmark agreement with Russian President Vladimir Putin to reduce each nation's nuclear arsenals to 1,700 to 2,200 warheads from the current 6,000 each is allowed.
The president also plans to tour Putin's hometown of St. Petersburg before traveling to Paris for talks with French President Jacques Chirac; Normandy, France, to commemorate Memorial Day, and Italy to witness a NATO-Russian agreement ceremony and visit Pope John Paul II.
The Russian Foreign Ministry said Wednesday the brief nuclear-reduction treaty is ready for the presidents' signatures. A separate document will address political and security priorities, including a section pledging cooperation on missile defense — an issue that once divided the two leaders.
Putin has allowed Mr. Bush to withdraw from the Anti-Ballistic Missile Treaty without strong objection. In return, the document will propose early missile warning systems and other measures to increase "predictability and trust," said a Russian diplomat who spoke on condition of anonymity.
A U.S. diplomat said one provision still being negotiated would have the United States pledging to share anti-missile technology with Russia. — science that Moscow might need to help combat terrorism. The document underscores how the U.S.-Russian relationship has been transformed by the terrorist attacks.
American relations with Europe also were altered by the attacks.
Already wary of Mr. Bush's anti-missile defense plans, his scrapping of the Kyoto environmental treaty and his reputation as a go-it-alone foreign policy novice, European leaders have a list of post-Sept. 11 complaints.
Those include the treatment of Taliban and al Qaeda prisoners at Guantanamo Bay, the perceived rejection of NATO's offer of military support, Mr. Bush's rejection of the International Criminal Court and new American tariffs on steel.
Schroeder has publicly praised Mr. Bush, even as other German officials demand more clarity on U.S. plans for Iraq.
"Military action against Iraq is not justified as long as it isn't certain that that Saddam supports or shelters al-Qaida terrorists," said Peter Struck, the leader in Parliament of Schroeder's Social Democrats.
Struck expressed "absolute understanding" for the Bush administration's determination to tackle the roots of terror.
"But it would be entirely wrong if Mr. Bush believed he must finish what his father started in Iraq," Struck told ARD television, in a reference to the 1991 Gulf War.
U.S. officials privately complain that Europe is soft and unreliable now that early war successes have yielded to tougher tasks.