Nato Secretary General Jaap de Hoop Scheffer has made an impassioned plea for member states to commit resources to existing operations, notably in Afghanistan.
By Paul Adams
BBC defence correspondent
Speaking in London, Mr de Hoop Scheffer said it was "simply intolerable" that he was forced to get out his begging bowl as a standard operating procedure.
Nato's members, he said, announced political decisions to undertake missions, but "then we suddenly find out that nations are not prepared to make available the necessary capabilities".
Nato has not provided extra personnel and equipment for Afghanistan
There is nothing new about Nato bosses complaining to members that they are not being given the wherewithall to do the alliance's work.
But this secretary general is clearly fed up with it.
Mr de Hoop Scheffer, like his predecessor, has made a number of strong speeches in the past, urging members to improve their contributions to Nato, but this speech, on the eve of the Istanbul Summit (which begins in just over a week), was unusually forceful.
And why the outburst? In a word, Afghanistan. With the government of Hamid Karzai barely able to extend its authority beyond the capital, Nato has still not provided the extra personnel and equipment promised several months ago.
"Given the vast quantities of personnel and equipment available to the alliance overall, we have to ask ourselves why we still cannot fill them," he said.
"What is wrong with our system that we cannot generate small amounts of badly needed resources for missions that we have committed to politically?"
Mr de Hoop Scheffer said Nato had to "devise a formula that both encourages and enables nations to honour their collective decisions and commitments".
The alliance had no choice but to deliver, making sure its means matched its ambitions, he added. He wants to reform the planning process.
De Hoop Scheffer feels allies have been distracted by Iraq
The allies, he said, should consider common funding of essential capabilities, like airlift and medical facilities.
He is also clearly worried that Nato leaders are thinking too much about Iraq at a time when they should be making good on their promises to Afghanistan.
Asked about Nato's possible role in Iraq, Mr de Hoop Scheffer said it would be wrong for members to start a discussion without first finding out what the new Iraqi government wants.
He also said he did not know if consensus on sending Nato troops to Iraq was achievable.
But he said that if the new Iraqi government asked for Nato's assistance, the alliance would not "slam the door in its face".