A strong Western defense is key to peace, NATO chief argues

''The mission that is assigned to us is to deter war. Now I define deterring war as maintaining peace.''

It was a statement with which most Americans, even those involved in the popular campaign to freeze the production of nuclear weapons, could agree.

Yet it came from Gen. Bernard W. Rogers, supreme commander of the North Atlantic Treaty Organization (NATO) - an articulate advocate of strong defense.

The goal of arms negotiations, he recently told a crowded seminar at Harvard's Kennedy School of Government, is to achieve ''verifiable and equitable arms control measures'' and a reduction in arms.

The route General Rogers advocates toward this goal includes a 4 percent real increase in defense spending from each NATO nation through 1990, as well as a rededication to what he calls the ''unity, cohesion, and solidarity'' of the alliance.

He notes that if Warsaw Pact forces attacked from an exercise at which they had mustered 50 divisions, NATO could at best respond with 29 divisions. Lack of conventional strength would severely limit NATO options: Alliance commanders, hard pressed to supply reinforcements rapidly from the US, would quickly have to decide whether to escalate the encounter to the level of theater nuclear weapons or to capitulate.