The Government will have to make "challenging decisions" about military priorities if the Nato-led Libya campaign continues beyond the summer, the head of the Royal Navy said.
First Sea Lord Admiral Sir Mark Stanhope also conceded that elements of the operation would have been cheaper and "much more reactive" if the aircraft carrier HMS Ark Royal had not been scrapped.
But he insisted he was not calling for the decision to axe the vessel and its Harrier jump jets - part of wide-ranging cuts to the armed forces announced last year - to be reopened.
Critics of the Strategic Defence and Security Review (SDSR) have seized on the lack of an aircraft carrier for the mission against Muammar Gaddafi's forces as evidence the SDSR was misguided.
But Defence Secretary Liam Fox said the UK's leading role in the intervention had shown it remained a serious military force and had the resources necessary to take part.
"How long can we go on as we are in Libya?", Admiral Stanhope told a media briefing. "Certainly in terms of Nato's current time limit that has been extended to 90 days, we are comfortable with that. Beyond that, we might have to request the Government to make some challenging decisions about priorities."
He continued: "If we do it longer than six months we will have to reprioritise forces. That is being addressed now. It could be from around home waters. I will not prejudge what that decision will be."
Harrier jets could have been deployed in 20 minutes rather than the 90 minutes taken to send Tornado and Typhoon aircraft from the Italian air base at Gioia del Colle, he pointed out. But he noted that they would not have been able to use Brimstone missiles carried by the other aircraft and insisted he was not "bitter" about the scrapping of Ark Royal.
"We have to look forward and go for what is in the pipeline which I have already indicated is challenging enough. There is far too much about what could have been as opposed to what is."
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Dr Fox said: "Operations in Libya are showing how capable we are post-SDSR as a leading military power with the fourth largest defence budget in the world. We continue to have the resources necessary to carry out the operations we are undertaking and have spare capacity with the Royal Navy Cougar Taskforce which is currently on exercise in the Gulf."
