The Government last week successfully played down a warning by the Liberal Democrat leader, Paddy Ashdown, of impending US pressure to do so. But in fact the issue has already reached the international agenda and could become a definitive test of Britain's status at the United Nations and in the world.
Last week, nuclear disputes involving Israel, the Arab countries, Iran, the US and Russia became public, complicating the process of winning votes for an indefinite extension of the treaty.
The NPT has for 25 years enshrined only five nations as "weapons states" - Britain, the US, France, Russia and China. It is due to be renewed at a conference in New York in mid-April.
British diplomats, headed by Sir Michael Weston, ambassador to the UN Disarmament Conference in Geneva, have up to now lobbied with apparent success to win the 86 votes needed to extend indefinitely the treaty by simple majority. But senior officials in Whitehall admit that the task has become harder than they first thought. "A majority of one is not much use," one diplomat said.
Another dimension has been added by President Boris Yeltsin's recent statement in favour of a so-called Start 3 disarmament pact that would radically cut the arsenals of Russia and the US to levels that would call into question the right of Britain and France to maintain their independent deterrent forces at planned strengths.
Foreign Office spokesmen spent much of last week denying a report in the Independent on Sunday, quoting Mr Ashdown, that Washington was about to press Britain to include its nuclear weapons in multilateral negotiations.
Privately, senior officials concede that the climate of discussion in Washington has become sufficiently volatile to permit the airing of radical new theories, both inside and on the fringes of President Bill Clinton's administration.
One important problem concerning British policy and the NPT renewal is that Third World states claim the NPT is not applied fairly. They point to Article IV of the treaty that says signatories "have the right to... the fullest possible exchange of equipment, materials and scientific and technological information for the peaceful use of nuclear energy."
Yet the US and its allies are intent on denying Iran, a signatory, technology for its nuclear programme. The US House Speaker, Newt Gingrich, says aid to Russia should be cut off if the Russians go ahead with a $1bn (£600m) contract to refurbish a reactor on the Gulf.
Last Sunday, Russia's Deputy Foreign Minister failed to persuade Iran to sign an indefinite extension. His Iranian counterpart, Mahmoud Vaezi, said Tehran was committed to sign but insisted that "corrections need to be made."
The Iranian issue, like North Korea, highlights the problem of enforcement under the NPT. It casts doubt on its effectiveness and shows up conflicts among the weapons states.
Western intelligence agencies are convinced that Tehran has a secret weapons programme, run by an shadowy inter-ministerial body, drawing members from the defence and nuclear ministries and reporting to the head of state, President Ali Khamenei.
But Tehran is making the most of its symbolic claim that the peaceful nuclear aspirations of a developing nation are being denied by an "imperialist" nuclear club.
In the past week, a dispute broke out also between Israel and Egypt at government level. Israel has not signed the NPT and claims it "will not be the first" to introduce nuclear weapons to the region. But the rest of the world believes Israel has at least 200 warheads and the Arab states show every sign of rejecting Western pressure to renew the NPT unless Israel is brought into the equation. The Israeli Foreign Minister, Shimon Peres, failed to defuse the argument in talks with President Hosni Mubarak.
"The nuclear issue cannot be sidestepped," an official commentary on Cairo radio said. "The peace talks should be linked to this pivotal issue."
These disputes inevitably focus attention on the most contentious claim of all. It is that the five weapons states wish to compel others to forfeit the nuclear option, while ignoring Israel's arsenal and themselves remaining in permanent violation of the NPT's Article VI.
This requires parties "to pursue negotiations in good faith on effective measures relating to the cessation of the nuclear arms race at an early date and to nuclear disarmament.''
The Campaign for Nuclear Disarmament (CND) has pointed out that Britain's Trident submarine programme will increase the number of British warheads by the end of the century. The Government responds that the overall explosive power will remain "not greatly in excess" of present levels and is the minimum credible deterrent. Whitehall also maintains the belief that "nuclear weapons cannot be disinvented".
CND says this logic conflicts with Britain's attitude to chemical weapons, which equally "cannot be disinvented". The UK has signed the Chemical Weapons Convention that bans such weapons and provides for their destruction.
The most important political point is that such critical attitudes are no longer the province of single-issue pressure groups or self-interested Third World dictatorships.
Germany, for example, is smarting over the rejection of its suggestion for a nuclear weapons register. Mexico's influential ambassador in Geneva, Miguel Marin Bosch, who chaired the preliminary NPT talks, spoke of widespread international ill-feeling.
Mr Bosch said the technologically advanced nations regularly reached a point where they could discard a weapon and then tried to ban that weapon throughout the rest of the world in a multi-lateral treaty.
"The nuclear weapons states should begin by committing themselves to the complete elimination of nuclear weapons by a certain date," he said.
CND has called for a compromise on the treaty, which may end up on the table if a convincing majority for the treaty's indefinite extension cannot be mustered. The compromise is to extend the NPT for a limited period that would be linked to a global nuclear disarmament process.
Since President Yeltsin's Start 3 proposal, the rules of the game have altered. The Foreign Office has said that "if there was a continuing reduction of strategic weaponry following treaties beyond the Start agreements, the point might come where we put ours into the equation."
Only hidebound diplomats could believe the point has not drawn nearer in the last week.