Britain could delay new nuclear submarines -BBC

* Ministers consider delaying Trident replacement - BBC

* PM's spokesman says "profile of expenditure" under review

LONDON, Sept 16 (Reuters) - The British government is considering delaying the replacement of its submarine-based nuclear missile system to put back big spending and defuse tensions in the ruling coalition, the BBC reported on Thursday.

Prime Minister David Cameron's spokesman would not confirm or deny the report on a sensitive issue which has also caused arguments between the Treasury and the Ministry of Defence over who should foot the bill.

"The position is that we will maintain the nuclear deterrent. Clearly, as part of that value for money review, I would expect us to be looking at the profile of expenditure," Cameron's spokesman told reporters.

Asked what he meant by "profile of expenditure", the spokesman said: "It means when you spend money".

The government is conducting a strategic defence review as well as a broader review of all government spending to find savings of tens of billions of pounds as it strives to slash a budget deficit running at 11 percent of national income.

The BBC reported that ministers were considering postponing the final decision on replacing the four submarines that carry the Trident weapons system from 2014 until after the next parliamentary election, which is scheduled for 2015.

That would mean putting back spending of at least 20 billion pounds ($31.2 billion), easing pressure from the Treasury on the Ministry of Defence to find massive savings in other programmes.

It would also please the Liberal Democrats, junior partners in the government, who campaigned against replacing Trident until they unexpectedly formed a coalition in May with the Conservatives, who strongly favour maintaining the programme.

The coalition agreement between the two parties states that Britain would maintain its nuclear deterrent but the renewal of Trident would be scrutinised to ensure value for money. Liberal Democrats would continue to argue for alternatives.

Speculation has mounted that Trident might be downgraded to make it cheaper, for example by replacing only three of the four submarines -- which would end the policy of having at least one submarine at sea all the time.

Jock Stirrup, outgoing head of the armed forces, expressed alarm on Thursday at such a proposal.

"I would be worried about any proposition that was untenable in the context of maintaining the minimum credible nuclear deterrent, which, to me, is continuous at-sea deterrence by a submarine," he told a parliamentary committee.

- For a story on defence firms being asked by government to review programmes, including Trident, click on [ID:nLDE6871VL] (Reporting by Estelle Shirbon; editing by Janet McBride)