President Barack Obama told Europe on Friday it must do more to help the United States win the war in Afghanistan, looking to leverage his huge popularity here to wring concessions from NATO allies.

Greeted like a hero by the crowds after flying into France for a NATO summit, Obama said he wanted to see a world without nuclear weapons, but warned Europe that it had to face up to the threat still posed by al Qaeda.

Obama announced last week he was going to dispatch more troops to Afghanistan as part of a new strategy to battle a growing insurgency that is spreading to neighboring Pakistan.

European leaders are reluctant to send more of their own soldiers to the war, preferring to focus their energies on civilian reconstruction and development projects.

Speaking in a U.S.-style town hall meeting before thousands f European youths, Obama said he supported these efforts but that the military operation needed more support.

Europe should not simply expect the United States to shoulder that burden alone. This is a joint problem that requires a joint effort, he said.

The United States has 38,000 troops in Afghanistan, more than all the other national contingents put together. Obama has said he will add an extra 17,000 U.S. combat troops as well as 4,000 others to help train Afghan officials.

Obama's Afghan plan aims to get a grip on rising violence by Taliban militants driven from power in 2001 but never completely defeated, broadening the focus to Pakistan and putting the highest priority on the defeat of al Qaeda militants.

Looking to engage skeptical Europeans, Obama said al Qaeda posed more of a threat to them than to the United States.

...It is probably more likely that al Qaeda would be able to launch a serious terrorist attack on Europe than on the United States because of proximity, he said.

French President Nicolas Sarkozy enthusiastically endorsed the strategy following talks with Obama, but made clear that France itself would not be adding to its 2,780 troop contingent.

There will be no French military reinforcements ... We are ready to do more in the field of policing, of gendarmes, in the field of economic aid, to train Afghans, he said, standing alongside Obama.

NEW IMAGE FOR USA

Although his message was sometimes tough, Obama himself presented a new image of the United States to Europe following the uncompromising presidency of his predecessor, George W. Bush, who was deeply unpopular on this side of the Atlantic.

The United States cannot confront challenges alone but Europe cannot confront them without America, he said.

He was greeted by cheering crowds when he arrived in Strasbourg, fresh from his economic diplomacy at the G20 summit in Britain, and was equally feted later on Friday when he traveled the short distance across the border to Germany.

The NATO summit is being co-hosted by former foes France and Germany and will be packed with symbolism aimed at celebrating an alliance originally created to defend Europe's borders.

Obama warned that although NATO's old adversary, the Soviet Union, had gone, the threat of nuclear catastrophe remained.

Even with the Cold War over, the spread of nuclear weapons or the theft of nuclear material could lead to the extermination of any city on the planet, he told the town hall meeting.

This weekend in Prague, I will lay out an agenda to seek the goal of a world without nuclear weapons, he said, referring to a EU-U.S. summit in the Czech Republic on Sunday.

The NATO summit starts with a dinner in Germany where talks will initially focus on often difficult relations with Russia.

It is important for NATO allies to engage Russia, and to recognize that they have legitimate interests, in some case we have common interests, but we also have some core disagreements, Obama said after talks with Sarkozy.

Discussions on Saturday will focus on Afghanistan with NATO Secretary-General Jaap de Hoop Scheffer urging U.S. allies to send up to 4,000 more troops to safeguard August elections.

This should not be exclusively President Obama's and the U.S. conflict in Afghanistan. That is, I think, an important political notion, also for the political balance in the North Atlantic alliance, de Hoop Scheffer told Reuters.

He is due to stand down as NATO chief in July. Danish Prime Minister Anders Fogh Rasmussen is the frontrunner to replace him, but Turkey is resisting, unhappy with his handling of a 2006 row over cartoons of the Prophet Mohammad that caused riots in the Muslim world.

I take a negative view (on Rasmussen's candidacy), Turkish Prime Minister Tayyip Erdogan said in London.

Germany Pakistan Afghanistan George W. Bush