David Cameron will honour his commitment to above-inflation rises in the defence budget after 2015, senior sources have indicated.
Tensions have been growing in the Coalition as negotiations begin over how to save billions of pounds more in the 2015-16 spending review.
Defence Secretary Philip Hammond, who has already seen his budget slashed by 8% in real terms since 2010, is believed to be among ministers resisting further cuts.
Tory backbenchers are among those voicing fears that the long-term capabilities of the military could be degraded unless more money is found.
The issue has been cast into sharper relief by the Government's commitment of up to 330 personnel and air support to the campaign against rebels in Mali.
Protecting Ministry of Defence budgets could mean harsher treatment for the police and other services.
However, it is understood the Prime Minister "does not resile" from comments he made in October 2010, when he appeared to accept that defence spending had to start rising again from 2015 onwards.
Mr Hammond said that he had been given a commitment that the equipment side of his budget - accounting for roughly half of MoD spending - would rise in real terms but that there would be a "robust discussion" about other elements.
"I have a firm commitment that the equipment plan, which is a very large part of the defence budget, will rise in real terms by 1% a year between 2015 and 2020, that's a commitment that has previously been made and repeated since the Chancellor delivered his Autumn Statement," he told BBC Radio 4's Today programme.
"But there is going to be a spending review for 2015/16 and I will go into that arguing the case for the resources that defence needs to deliver the plan that we have set out, Future Force 2020, and I am very confident that we will have a robust discussion about that."