Gordon Brown has come under pressure over Trident renewal
Lib Dem leader Nick Clegg has attacked government "chaos and confusion" over renewing the Trident missile system.
No 10 has insisted the timetable for renewing Trident is unchanged.
But earlier, officials implied that key decisions would be put off until May 2010 ahead of a conference on the Nuclear Non-Proliferation Treaty.
Mr Clegg said the prime minister should make a "climbdown" and admit the missile system was not justified given equipment shortages in Afghanistan.
In a statement, Downing Street said there had been "no change" in the government position that Trident would be renewed.
The Ministry of Defence also insisted the policy was unchanged.
But earlier on Thursday, an official briefed the media that the UK's nuclear deterrent was "now up for grabs" in the context of a multilateral disarmament agreement.
The statement from No 10 was issued as the prime minister set out a "road map" for disarmament in which all nuclear states would pledge to reduce their stockpile of warheads.
Gordon Brown is under pressure over plans to renew the UK's own nuclear weapons.
The prime minister says he is committed to updating the Trident submarine-based missile system despite its estimated £20bn cost.
'Unnecessary and unjustifiable'
Mr Clegg said the government had "rammed the decision to renew Trident through Parliament without a proper debate".
He added: "The chaos and confusion surrounding Gordon Brown's machinations on Trident is staggering.
"Gordon Brown should now complete his climbdown and admit that a like-for-like Trident replacement is unnecessary and unjustifiable when our troops in Afghanistan are still short of kit."
The decision to postpone spending decisions until after May 2010 would have effectively pushed them up to or beyond the next general election at a time when government finances are extremely tight.
In briefings, the official stressed that the decision to replace the Trident system had been taken in 2006, but the "world had changed" since then not least with the election of US President Barack Obama, who has made disarmament a priority .
The official said: "All our deterrent is now up for grabs but in the context of a multilateral negotiation."
By the "sequencing of expenditure" on Trident, as the official put it, the decision could essentially be "pushed back".
But the official said progress on nuclear disarmament had to be "multilateral" and the goal of a nuclear free world had to be seen as an "aspiration".
However, Downing Street issued a statement which read: "The policy remains as set out in the 2006 White Paper, and there has been no change to the timetable."
A spokeswoman for the Ministry of Defence said: "There has been no change in the government's position on Trident.
"The policy remains as set out in the 2006 white paper, and there has been no change to the timetable."
The series of briefings came as Mr Brown outlined plans to offer assistance to countries such as Iran to develop civil nuclear power in return for assurances they will not build bombs.
Mr Brown has ruled out unilateral cuts to either the Trident submarine fleet or the UK's 160 warheads and has called for collective action to stop nuclear proliferation.
He set out his proposals in a written statement to MPs designed for debate ahead of talks next April designed to pave the way for a review of the International Non-Proliferation Treaty.
The Lib Dems have called for Trident to be scrapped in favour of a less expensive system while the Conservatives, who support Trident, says its future must be considered as part of a comprehensive defence review.
Some 95 Labour MPs -including 16 former ministers and four ex-members of the cabinet - rebelled against the government during a vote on renewing Trident in 2007.
A document released by the Cabinet Office on the same day stated that the government continued to judge "that a minimum nuclear deterrent remains an essential element of our national security".