score:5
As @T.E.D. has pointed out in the comments, NATO almost certainly had top-level planning to cover that contingency, but it is extremely unlikely that NATO ever seriously considered starting a war unilaterally.
Some idea of NATO's strategic planning can be found in the review of NATO Strategy Documents, 1949-1969. These strategy documents show that the focus of strategic planning was always on defence. Indeed, it is unlikely that the electorate in the western democracies that formed the core of NATO would have supported an unprovoked attack on the Warsaw Pact nations.
Furthermore, the principle of collective defence is at the very heart of NATOβs founding treaty. It is enshrined in Article 5 of the Washington Treaty. In essence, this states that an attack against one Ally is considered as an attack against all Allies. The treaty made no provision for starting a war unilaterally, and it is by no means certain that all the member states would have gone along with any such military action.
We do know, however, that plans for a nuclear first strike against the Soviets were drawn up for JFK during the 1961 Berlin Crisis. How detailed those plans were remains unclear, but it doesn't appear that other NATO allies were involved.
The fact that a nuclear first-strike was being considered, rather than an invasion by conventional forces of the type you describe in the question, does appear to correspond with the evidence from the NATO Strategy documents. There was no provision in place for an unprovoked attack by NATOs conventional forces at that time.