The RAF will need "genuine increases" in its budget over the coming years if it is to run the range of operations ministers demand, its chief has said.
Air Chief Marshal Sir Stephen Dalton told the Guardian the RAF was stretched to the limit, with operations over Libya planned for at least six months.
The Army and Royal Navy will set out details later of the first wave of job losses from October's defence review.
Ministers have denied the review was simply a "cost saving exercise".
ACM Dalton said his assumption was that the RAF's warplanes and surveillance aircraft would be needed over Libya for a number of months, rather than weeks.
"In general terms [we] are now planning on the basis of at least six months, and we'll see where we go from there," he said.
He issued a warning that the RAF would need an increase in spending from the next Comprehensive Spending Review in 2014.
Without "genuine increases", he said the RAF would find it "very difficult" to maintain its current levels of capability - with operations in Afghanistan, the Falklands and Libya.
"The key factor is that if we are to meet the requirements laid upon us, there is no question that more investment will be needed to achieve that.