In an East Room news conference with leaders of the European Union, the president did not spell out how far he would go to prevent Iran from joining the nuclear club.
"Iran must comply. I mean, the free world expects Iran to comply. Just leave it at that," Bush said. "We believe they will when the free world comes together."
He then talked over his counterpart to finish his thought: "And if they don't we'll deal with that when they don't."
Hoping to heal division caused by Iraq war, the leaders touted their agreements to curb funding to terrorism organizations and hasten extradition of terrorists.
"When Europe and United States are united no problem and no enemy can stand against us," said Romano Prodi, president of the European Commission. "If we fail to unite every problem may become a crisis and every enemy a gigantic monster."
"Many people have said that Europe is too old," Prodi said, a reference to Defense Secretary Donald Rumsfeld calling anti-war allies part of "old Europe." Said Prodi: "Maybe, but the old age helps us to understand our strengths and our weakness."
Bush replied with a smile, "You're looking pretty young these days."
Greek Prime Minister Costas Simitis, whose country holds the rotating EU presidency, said, "What unites us always outweighs what divides us."
The president saved his harshest words for the militant Palestinian group Hamas.
"In order for there to be peace in the Middle East, we must see organizations such as Hamas dismantled," he said.
The president reacted skeptically to reports of a three-month halt on attacks on Israelis by three Palestinian militant groups. "I'll believe it when I see it," he said.
At the Justice Department, Attorney General John Ashcroft and the Greek Minister of Justice, Philippos Petsalnikos, signed updated and expanded extradition and mutual legal assistance agreements between the United States and EU.
The treaties broaden the number of crimes to which extradition will apply and authorize such things as joint investigative teams, video testimony in court cases and sharing information on suspect bank accounts.
"These treaties focus not on our differences, but on our common values," Ashcroft said.
Bush said the leaders had agreed to monitor the nuclear ambitions of North Korea and Iran.
"Iran has pledged not produce nuclear weapons and the entire international community must hold that regime to its commitments," he said.
Bush said he believed the nation would give up its nuclear hopes once the international community raises its voice.
"If the world speaks together, they'll comply," Bush said.
Pressed for what action he would take should Tehran refuse to bow, the president said, "If they don't, then we'll deal with that when they don't."
For years, this meeting attracted little attention on either side of the Atlantic. This time, however, relations are at a historic low because of differences over the Iraq war and what Europeans see as Washington's disregard for allies' views.
There is new impetus to pull together. The European Union and the United States, along with Russia and the United Nations, jointly drafted the "road map" that they hope will lead to Middle East peace.
Greek government spokesman Christos Protopapas said the Europeans hoped the summit would "constitute the starting point for a new era in the strategic partnership between the United States and Europe after the tension that existed in recent months."
But there are other issues besides Iraq that divide the United States and the Europeans.
Europe has stuck by its 1998 moratorium on the import of genetically modified foods because many European consumers fear health risks. Bush has scolded them for that stand in recent weeks, charging that it is worsening famine in Africa by discouraging African nations from investing in biotechnology.
The moratorium costs American farmers an estimated $300 million a year in lost corn exports alone. The United States plans to take the dispute to the World Trade Organization.