Baroness Falkner told a fringe debate on Trident at the LibDem party conference in Glasgow that the country deserved a real debate on the issue.
The LibDems have called for a scaled-back replacement for the ageing nuclear weapons system on the Clyde.
A Whitehall review overseen by the party found that the UK could be protected while giving up round-the-clock nuclear patrols.
Delegates will this week debate a party paper based on the review, led by Danny Alexander, the LibDem Chief Secretary to the Treasury.
But Baroness Falkner told the packed fringe event that not only did the paper mention unilateral disarmament, but "you could be forgiven for thinking the LibDems want (such an option) but are not really prepared to say it".
She added that the LibDems "owed the country" a debate over the issue.
And the peer warned that sending out unarmed boats, one of the options which were put forward under the LibDem's proposals, would "not make (Russian president) Putin quake in his boots".
At the same debate Mr Alexander insisted there was a "clear intellectually coherent and morally right argument at the heart" of his party's position.
Prime Minister David Cameron has made clear his opposition to the plan, insisting the Tories are committed to a "like for like replacement" for Trident.