Defence secretary Philip Hammond has branded his Liberal Democrat colleagues "reckless" for considering a downgrade to Britain's nuclear deterrent.
His criticisms came ahead of tomorrow's publication of the Trident alternatives review carried out by the government.
The paper will not come to any conclusions on the like-for-like renewal of Trident, which is set to receive its final confirmation from ministers after the next general election.
But it is expected to provide the Lib Dems with enough firepower to argue the case for a cheaper, more cost-effective nuclear deterrent.
Hammond's article for the Mail suggests building three nuclear submarines instead of four would save less than 0.17% of the annual defence budget over their lifetime, however.
"There will be those who seek to use this review to argue that, even if we continue with Trident, we can downgrade to a part-time deterrent – claiming that our potential adversaries will always give us months of advance warning of an intention to strike," the Tory defence secretary wrote.
"I believe that taking such a risk would be reckless... How can anyone be confident that the global security environment will not change in the next ten years? This is not the time to let down our guard."
Conservatives have worked hard to take on the Lib Dems over Trident, seen as a clear dividing line between the two parties in seats where they will fight each other in 2015.
David Cameron used a newspaper article to warn of the threat posed by North Korea in April. He insisted the cost of Trident was not prohibitive in a time of austerity, saying it was less than 1.5% of our annual benefits bill.
But deputy prime minister Nick Clegg has continued to insist "there are options", telling journalists at his first monthly press conference last week that "a system designed for the Cold War" could be revised.