He was speaking after his party conference voted to confirm the Liberal Democrat policy of opposing a like-for-like replacement, and its Armed Forces Minister Nick Harvey said such a delay would have a "profound political significance".
Mr Clegg told BBC Radio 4's The World at One: "I have always argued we should be looking at alternatives to a like-for-like replacement for Trident.
"This is a live debate and we will need to arrive at a decision on all these things, on timing, and cost and detail, between now and the Comprehensive Spending Round (CSR).
"It's a perfectly sincere, level-headed debate about what are the security threats the country faces in the coming period."
He added: "Given that we are fighting a war in Afghanistan, given that we will no doubt have to fight other conflicts in the future, it begs questions about how you can stretch the MoD budget."
Mr Clegg said the timing of a decision on replacing Trident was "linked to other decisions that are very pressing in the MoD".
The CSR is due to report on October 20, and Mr Harvey told the Lib Dem conference today that the "main gate" decision on the nuclear deterrent - the "point of no return" - is currently scheduled for the end of 2014 or the start of 2015.
But he went on: "If it were to be delayed until just after the May 2015 election, it is of no great financial significance, it is of no great military significance, it is of no great industrial significance.
"But believe me, it is of profound political significance.
"Conservatives know that they are not going to be able to look to the Liberal Democrats to get that through Parliament, so the issue will be a hot potato for Labour."
The Tories are committed to a like-for-like replacement for the submarine-based missile system, as was the previous Labour administration.
Lib Dem members in Liverpool voted unanimously for a policy motion calling on ministers to allow a full review of alternatives to the like-for-like replacement to be included in the Government's Strategic Defence and Security Review.
Labour MP John Woodcock, in whose constituency of Barrow and Furness the replacement Trident submarines would be built, said: "New Lib Dem defence minister Nick Harvey is brazenly admitting to playing politics with Britain's national security - that is the height of irresponsibility from the new Government.
"Last week Mr Harvey reassured his new friends in the House of Commons that he 'wasn't aware of any suggestion to delay decisions on Trident' and said the timetable had been decided.
"But he has immediately reverted to type in front of his supporters and said the Government may delay decisions on Trident purely for political reasons.
"That shows the lack of principle at the heart of the new Government and highlights the risk to the British people that this mix of Conservatives and Liberal Democrats represents."
Kate Hudson, general secretary of the Campaign for Nuclear Disarmament (CND), welcomed the Lib Dem debate and vote.
"The Liberal Democrats have strongly reasserted their policy on Trident and it is now clear that they will pursue those goals," she said.
"We now hope that Lib Dem ministers will vigorously pursue the outcome of this motion to ensure Trident is indeed included in the Strategic Defence and Security Review."
Shadow defence secretary Bob Ainsworth said: "This is a completely immature way to decide our future defence and security policy.
"The Government must make those decisions in the best interests of our country, not delay them just to score political points. Putting off difficult decisions shows just how weak this coalition is.
"The Liberal Democrats needs to grow up and start acting like a responsible governing party."
Mr Clegg stressed later that the cost of replacing Trident would have to be borne by the Ministry of Defence - something which has been resisted by Defence Secretary Liam Fox.
The Deputy Prime Minister was asked about the issue by a student as he took questions at New York University.
He acknowledged there were "differences" on the issue within the coalition but said ministers would be trying to overcome them with "an approach we are all happy with".
"The renewal of Trident is a very expensive thing to do which would have to come out of the Ministry of Defence," he said.
Comments