Leading article: Dangers that lurk when Nato's ambition exceeds its grasp

However the Government and the top brass envisaged the Libya mission at the outset, it is hard to believe that they calculated with great accuracy where it would be today. Three months in, British, French and other forces are still engaged in pretty much the same sort of operations as they were at the start. Benghazi might be safely in the hands of the anti-Gaddafi opposition, but the fight is still on for Misrata. And while British ministers have increasingly stretched the UN Security Council mandate to presuppose the demise or departure of Muammur Gaddafi, the situation on the ground is described most often as a stalemate. Gaddafi has not routed the opposition, but nor has he been defeated.

In such circumstances, discontent and impatience are naturally coming to the surface. Libya's rebels are unhappy with the level of support they are receiving, even though the UN resolution provided only for the protection of civilians. They are also, quite reasonably, distressed – as Nato and the forces responsible must be – about recent targeting errors (so described by alliance spokesmen) that have resulted in the deaths of civilians.

Among the foreign forces, the French apparently want the whole operation done and dusted by Bastille Day (14 July); the Danes are reported to be running low on bombs, and the Italian foreign minister has called for a ceasefire to permit the delivery of aid. In the United States, President Obama – whose attention is fixed on Afghanistan – faces persistent questions about the lack of Congressional approval for the action, while fading public support in Britain has been accompanied by expressions of unease by commanders, who argue that resources are being spread too thin. Even the Arab League, whose initial plea has often been cited by the Prime Minister and the Foreign Secretary as having clinched the argument for intervention, seems to be getting cold feet and has joined the Italian ceasefire call.

Of all the representations, those of the British commanders are the most easily dismissed. Mr Cameron was right when he said somewhat caustically that he would "do the talking" and the military should "do the fighting". Having given their advice, and presumably accepted the mission as feasible, they cannot now turn around and call foul. The suspicion must be that they are exploiting the perhaps unforeseen duration of this conflict to lobby for a reversal of the Government's spending cuts. To which the response must be that this is neither the time nor the place.

The other temptation to be resisted at all costs is any extension of the mission. Not only is there zero chance of getting a new and tougher resolution through the UN Security Council, but there has been quite enough mission creep already, what with the continuing vagueness of British ministers about whether Gaddafi himself is a target and the recent deployment of Apache helicopters. The outgoing US defence secretary, Robert Gates, spoke the salutary truth, when he told Europeans that if they wanted a military capability to match their operational ambitions, they would have to pay for it – or keep their ambitions within bounds.

Libya, it increasingly appears, may turn out to be where idealism – the prevention of a massacre in Benghazi and a desire to keep alive the spirit of the Arab Spring – meets reality, the recognition that there is neither the money nor the mandate to achieve much more. There can be no question of abandoning the opposition forces to their fate. But if, as it seems, they need more help to speed their victory – beyond the UN-authorised protection of the civilian population – then this intervention may be reaching its limits and the only option will be some hard bargaining about the shape of a post-Gaddafi settlement.