"I am frankly concerned when I hear the United States is planning a major commitment for Afghanistan, but other allies ruling out doing more," he said at the security conference in southern Germany.
"That is not good for the political balance of this mission. That is not good for the balance inside the North Atlantic alliance," he said. "Leadership and burdens -- they go together."
Scheffer, who did not single out any nation, warned that the failure to step up "makes calls for Europe's voice to be heard in Washington perhaps a bit more hollow than they should be."
New US President Barack Obama has singled out Afghanistan as his main front in the "war on terrorism" and plans to deploy 30,000 more US troops there over the next 18 months.
The North Atlantic Treaty Organisation is embarked on its biggest and most-ambitious operation ever trying to spread the influence of the weak Afghan government across the strife-torn country and help foster reconstruction.
But the Taliban and its backers, including Al-Qaeda, drug lords and criminal gangs, have been waging an increasingly tenacious insurgency and seriously undermining NATO's goals.
Britain, Canada, the Netherlands and the United States have troops on the frontline of that fight in southern Afghanistan, but other allies insist that reconstruction is as important as combat and refuse to redeploy.
Germany, which has troops based in the north of the country, has been reluctant to sent troops to the south, where fighting is more intense. The Afghanistan mission is not popular with the German public and Chancellor Angela Merkel has said Germany is already doing its part there.
On Wednesday, Britain also scolded its NATO allies for not stepping forward to share combat duties, warning that there could be no freeloaders in the fight against the insurgents.
"An alliance worth its name must be one that shares the burden of membership equally amongst its members, because there can be no freeloading when it comes to collective security," British Defence Secretary John Hutton said.
"Volunteering, not waiting to be asked, must be the hallmark of a proper relationship between the transatlantic members of this alliance," he told NATO ambassadors.