Gareth Evans has warned signing up to the international campaign to abolish nuclear weapons will “tear up” the United States alliance ahead of a critical contested vote in an otherwise tranquil Labor conference.

The former foreign affairs minister made the comments to Guardian Australia on the sidelines of Labor’s national conference, intervening in a dispute over how to translate in-principle support for disarmament into practical action.

The showdown set for Tuesday pits the Labor frontbencher Anthony Albanese against the party’s foreign affairs spokeswoman, Penny Wong, two traditional Labor left allies divided by conditions to be put on joining the treaty.

Guardian Australia understands that Albanese has registered an amendment proposing to sign and ratify the nuclear weapons ban treaty immediately to send a strong signal in favour of disarmament and noting that Australia can seek changes after it joins.

Wong and the party’s defence spokesman, Richard Marles, proposed instead that conditions should be imposed before Australia signs up.

Conditions that were considered included: a verification regime, which the ban treaty currently lacks; consistency with the nuclear non-proliferation treaty, which is disputed; and universality, an almost insurmountable barrier given the fact no nuclear states are signatories.

It is unclear whether the disarmament fight will be contested in a vote on Tuesday, the final day of Labor’s conference. An earlier vote on Monday against creating a statutory human rights charter led the Labor right to believe it commands the numbers to support Wong and Marles’ position if the nuclear weapons ban treaty is put to a vote.

Evans said “disarmament – as distinct just from non-proliferation – is core business for any Labor government and I’m passionately in favour of disarmament”.

He said the treaty is a “hugely significant” development setting a moral norm against nuclear weapons, and “in-principle it’s hard to contest”.

“The difficulty for Australia in terms of signing or ratifying the ban treaty is that, to do so, we would effectively be tearing up our US alliance commitment.”

Evans cited section 1E of the treaty, which prohibits signatories from doing “anything to assist” a nuclear weapons state in activities including stockpiling them as a deterrent.

Evans said, if it signed, Australia would be banned from assisting the US through the north-west cape installation and Pine Gap, which are “critical components of the alliance relationship” used to communicate and coordinate with nuclear submarines in the US arsenal.

“As much as I would love to be supporting in neon lights the treaty – it’s just not a realistic position for Australia to be supporting it.”

Instead Australia should reduce risk by calling for reduced numbers of nuclear weapons, a doctrine of no first use, de-alerting and reduced deployments, Evans said.

“We should be working to create a nuclear weapons convention that the nuclear-armed states could themselves sign on to – which they can’t at the moment, it’s hopelessly impractical – one that provides for step-by-step commitments rather than all or nothing commitments,” he said. “There’s no way you can commit us to sign and ratify.”

Gem Romuld, ICAN Australia director, said: “Before Australia joined the treaty banning landmines Gareth Evans labelled it ‘hopelessly utopian’.

“That treaty is now considered a huge success with 164 state parties. Evans was wrong then and he is wrong again now on the nuclear weapon ban treaty.”

Australia has consistently refused to support or sign the ban treaty – supported by 122 countries – arguing that it relies on the protection of the United States nuclear umbrella.

A paper by the International Human Rights Clinic at the Harvard Law School, published in December, concluded if Australia signed the treaty it would have to leave the nuclear umbrella but the US-Australia alliance is otherwise legally compatible with it.

With nuclear weapons states modernising and in some cases increasing their arsenals, more states are becoming disenchanted with the nuclear non-proliferation treaty and lending their support to an outright ban.

According to Ican, 78% of the federal Labor caucus have pledged to work for Australia to sign and ratify the treaty, including two-thirds of the shadow cabinet.

Romuld said Labor “has a long and proud history of work around nuclear disarmament” .

“The nuclear ban treaty presents Australia with a choice: we either continue supporting the potential use of these weapons of mass and indiscriminate destruction or we make our nation and our world safer by joining the ban.”

In October Wong told the Australian Institute of International Affairs that the ban treaty has “significant shortcomings” although she strongly shares its objective.

Wong noted the treaty is a “clear declaration of the will of the majority of nations” but warned an “incomplete consensus against the possession and use of nuclear weapons is not enough to achieve a nuclear-free world”.

“A treaty banning nuclear weapons will have no effect without the support of those states that possess them,” Wong said, adding that there was “no prospect” of existing nuclear weapons states signing or ratifying the treaty.