The Liberal Democrats would “maintain a credible nuclear deterrent” if they won power, leader Tim Farron says.
“Our nuclear deterrent keeps us at the top table in this post-Brexit world,” he said.
But Mr Farron also advocated replacing the current system of continuous-at-sea deterrence with more irregular patrolling patterns.
And he accused Labour leader Jeremy Corbyn of being “weak and dangerous” on defence matters.
Earlier this week, Mr Corbyn – a long-standing opponent of nuclear weapons – said “all aspects” of defence would be reviewed if he won power in the snap election on 8 June.
“I have made clear there would be no first use of it and that any use of nuclear weapons would be a disaster for the world,” he told Andrew Marr on BBC One.
His party, however, issued a statement later the same day clarifying that Labour as a whole was in favour of renewing the existing Trident nuclear weapons system.
MPs overwhelmingly voted earlier this year to build four new submarines to carry missiles armed with nuclear warheads. They are intended to replace the existing Vanguard fleet from the early 2030s at an estimated cost of £31bn.
Mr Farron was expected to make his comments in a speech to supporters in Portsmouth, but the Lib Dems said the visit had to be cancelled due to unforeseen circumstances.
The pre-released text of his speech said: “If you say that you would never press the button, as Jeremy Corbyn seems to have suggested, that makes a mockery of having a deterrent or indeed sound defences.”
He added that the Liberal Democrats are committed to Nato, the European Union and the United Nations.
“We believe that our safety and security as a country is best achieved through co-operating with the UK’s allies,” he said.
“That is why we are committed to maintaining a credible nuclear deterrent, because there is nothing to gain from walking away from the table and turning our back on those who rely on our protection.”
Switching from a continuous at-sea deterrent to irregular patrols “would maintain the ability to surge to more frequent armed patrols, or drop down to a low-readiness posture if the security situation allows”, he argued.
Mr Farron also said the party’s long-term goal will “always be a nuclear-free world”, and it would use the UK’s position to lead international efforts towards multilateral disarmament.
The Lib Dems have faced division on the issue in the past, with some activists calling for Trident to be axed, saying it is expensive and unnecessary.
A commitment to replacing Trident was a Conservative manifesto pledge in the last general election in 2015.
And shortly before becoming prime minister, Theresa May said it would be “sheer madness” to give up the UK’s nuclear weapons because of the threat posed by other countries including Russia.