While I cannot speak for what the exact plan for conventional forces was in any given timeframe during the Cold War, the assumption is that the US Army in Berlin would fight in place until they were: relieved, overrun, or could conduct a breakout and pass friendly lines. A fascinating tool that would sustain the longevity of the Berlin Brigade was the Detachment A, 39th Special Forces Group. This unit, in the event of hostilities, would be tasked with conducting harassment and demolitions missions in order to stall and reroute Soviet maneuver units and reinforcements into Berlin. In the event of the overrun of West Berlin, the unit would conduct “Stay behind operations”, essentially, sabotage missions and organizing armed resistance. This is important as from the 60’s onwards, the REFORGER exercises continuously built upon NATO’s ability to mass forces on NATO’s Western flanks, however one of the prevailing defense plans to evolve as the Soviet’s weapons lethality became more readily visible (Soviet designed weapons were showcased heavily during the wars in the Middle East) was that of an active defense. In the active defense role (Particularly near the Fulda Gap, though this has been argued to NOT be the most important crossing point for Warsaw Pact forces for a myriad of reasons; it was one of the most obvious routes to score a potentially decisive victory against American ground forces however) NATO would essentially utilize screening forces to orchestrate a fighting-retreat to established fallback positions at the River Rhine. This is partly why we can look at our history and see inventions such as the Honest John Rocket, Davy Crockett recoilless munition, ADMs, MADMs, and the Mk-54 SADM, essentially the suitcase nuke. These atomic weapons were the initial answer to halting Soviet armor formations chugging westward (This period in time also spurned the creation of the M1 Abrams MBT, the AH-64 Apache attack helicopter, the A-10 Thunderbolt II, the F-117 Nighthawk, Star Wars, and many more). An additional factor complicating NATO’s presumed ability to halt a Soviet advance and form a swift counterattack was the reported increasing lethality of Soviet Air Defenses, which made the probability of employing a fighting retreat more likely as the Cold War progressed and weapons systems became increasingly sophisticated. I believe that a reasonable conclusion can be made that though the Berlin Brigade was combat equipped and mission capable, the expectation would be to fight in place and collapse inward with French and British forces in Western Berlin, breaking out westward when tactically feasible.