"To succeed in Afghanistan, Nato allies must provide the forces Nato military commanders require," Bush said in the Estonian capital, Tallinn, on his way to the meeting in neighbouring Latvia.
Altough all 26 allies have troops in the 32,800-strong force, Britain, Canada, the US and others in the south have complained that Germany, Italy, Spain and France keep their troops in the more peaceful north and west.
The US president called on member states to scrap the numerous caveats that prevent their forces from fully engaging in the Afghan mission.
he said: "While we have to be frank about the risks, we also have to avoid over-dramatising the difficulties."
|Taliban fighters have intensified their|
campaign against Nato forces
NATO commanders are also frustrated by around 50 caveats, which range from geographical restrictions - the biggest problem - to the refusal to fight at night or in winter conditions.
The British prime minister, Tony Blair, has also urged Nato to do more in Afghanistan.
He told a news conference held with Anders Fogh Rasmussen, the Danish prime minister: "NATO's credibility is at stake here. If we don't succeed in Afghanistan the whole of the world will be less secure."
Jacques Chirac, the French president, has called for a "contact group" to be formed of countries neighbouring Afghanistan and those involved in the Nato mission.
Chirac, writing in Britain's Guardian newspaper, said such a group was "necessary to give our forces the means to succeed in their mission in support of the Afghan authorities, and refocus the alliance on military operations".
Chirac wrote: "The Europeans have relied on their American allies for too long ... They have to shoulder their share of the burden by making a national defence effort commensurate with their ambitions for Nato and also for the EU."
Scheffer voiced support for Chirac's plan, saying: "We a need a body like the ... contact group in Kosovo that brings the key international actors together on a regular basis and coordinates overall strategy."
According to an unnamed senior French official, Chirac will say that in future, French troops could be deployed around the country when they are needed to help their Nato allies.
In early September, US General James Jones, Nato's military commander, called for 2,500 extra military personnel for southern Afghanistan - about 1,000 combat troops supported by 1,500 logistical and other staff - but they have not yet been provided.