International summit split over cost-cutting exit strategy that would see security forces radically depleted as soon as West leaves

The blueprint for the West's exit strategy for the long war in Afghanistan is being set out in a critical meeting, with military officials and diplomats battling to prevent a proposed depletion of Afghan forces while the security situation remains precarious.

The conference in Brussels took place as an American newspaper published photographs yesterday of US soldiers next to the dismembered bodies of Taliban suicide bombers. The Defence Secretary, Leon Panetta, had to apologise to the Afghan delegation and fellow Nato ministers for the way the reputation of international forces had been "besmirched" by the actions apparently depicted in the pictures published in the Los Angeles Times.

The Independent has learnt that military commanders and diplomats have been arguing against an early cut of almost 40 per cent in the size of Afghan forces, just when they are supposed to be taking over security responsibility from Nato.

Under one proposal which was being considered, the numbers would shrink from 352,000 to 220,000 from 2014. The primary reason is cost: cutting manpower would lower the country's annual defence budget, which the international community will have to fund, from $6.2bn (£3.9bn) to $4.1bn.

However, senior diplomatic and military sources say they are increasingly confident that the cuts, which they say would have a hugely damaging effect at a particularly sensitive time, can be delayed.

The timetable, however, remained unclear after yesterday's meeting. The British Defence Secretary, Philip Hammond, said: "I think the intention is that the numbers will run through 2014, through 2015, and will then start to go down to get to the target number of 228,500, which will be achieved by the end of 2017. So the number will be achieved over a couple of years."

Mr Hammond added that the UK will provide $110m of the $1.3bn requested from Nato members towards the funding of Afghan forces. Washington will contribute the bulk of the remaining $2.7bn.

However, Nato's Secretary-General, Anders Fogh Rasmussen, pointed out that the decision on the timing of the depletion of Afghan security forces has not been decided and would depend on the security situation in the country. "Together with the rest of the international community we will play our part and pay our share in sustaining Afghan security forces at the right level for years to come," he said. But, he added, there was a consensus that the long-term strength "would be around 230,000".

Nato commanders concerned about the effect of too quick a cutback have received support in the US Congress. The dangers involved were raised with the US General John Allen, commander of the International Security Assistance Force, when he appeared before the Senate Armed Forces Committee in Washington. Senator Carl Levin, the chairman, asked: "Given that transition to a strong Afghan security force is the key to success of this mission, why [are we talking] about reducing the size of the Afghan army by a third?"

Yesterday in Brussels, Mr Panetta praised the actions of the Afghan forces during a fierce insurgent assault on Kabul last Sunday. "They moved quickly and effectively because of the training we had given them," he said.

A senior British officer said: "This is precisely why we must be careful about the message we send. Is it really wise to tell these guys risking their lives that they may lose their jobs a little down the line? Do we really want 120,000 disaffected men – trained to use arms – made unemployed, out on the streets, in an economy highly unlikely to find them other jobs?"

The Afghan Defence Minister, General Abdul Rahim Wardak, said: "Nobody can predict the security situation after 2014. Going lower on troop numbers has to be based on realities on the ground. Otherwise it will put at risk all that we have accomplished together with so much sacrifice."

However, the security situation will be considerably affected by the actions of Gen Wardak's government, diplomatic sources pointed out. Afghan national elections are currently scheduled for 2014 – after international forces have left.

The elections in 2010 were beset by violence despite the presence of tens of thousands of Nato troops, and President Karzai is considering bringing the next elections forward to next year. But that has led to accusations that he may also be attempting to manipulate the country's constitution in order to run for a third time.

"Even if he does not run, as he keeps on saying, any hint of the kind of corruption we had the last time would lead to great anger and also trouble," said an American diplomat. "Security is much improved, but we have to accept that pretty risky times lie ahead."

Nato Chiefs & Politicians At War Over Risky Afghan Withdrawal Plans