LISTEN closely to the candidates and read the papers and the words pop up: Grenada. Revolution in Central America. Gromyko to meet Reagan. Soaring defense costs. ''War and peace,'' in other words, appears once again to be emerging as a major issue in the 1984 presidential election. That is as it ought to be.
Surely, President Reagan and Walter Mondale have a responsibility to explain to the American people how they would go about ensuring that the nation's military structure is appropriate to the nation's defense needs.
The two candidates should discuss how their overall defense strategies fit into a larger global foreign policy framework designed to actually prevent global conflict - particularly nuclear conflict - and ensure world peace.
The ''defense'' issue is clearly different this year from four years ago, when then-challenger Ronald Reagan rode into office with strong public yearning for an American military buildup. That public momentum for a stronger defense started in the late 1970s, and peaked, according to opinion polls, around 1980. And the post-Vietnam buildup had actually begun under President Carter.
Today, the US public still favors a strong defense. But the mandate for massive defense spending has fallen considerably since the late 1970s and early '80s, in part because of adverse reaction to allegations of mismanagement and cost overruns and, in part, because of a feeling that the tide has been turned - that America is now far stronger and better prepared for any use of military power than was true in the late 1970s.
There is another reason for taking a hard look at defense: costs. Bluntly put , they are considerable, given the size of federal budget deficits projected to run in the $200 billion range annually during the years ahead. This week, lawmakers are working on the defense budget for fiscal year 1985. It runs around increase in defense spending.
Can that be done without endangering the nation's security? This is an issue on which the views of economists as well as defense experts should be heard, because of the size of the deficits. In this sense, Walter Mondale did the nation a service by spelling out his plan to modify defense spending. By just holding down the rate of defense spending to between 3 and 4 percent annually, as he urges, some $25 billion in federal outlays would be trimmed from the budget by 1989. His total dollar outlays for defense, it should be noted, are very close to those of Mr. Reagan. Reagan will surely want to show how his slightly higher rate of defense spending - some one to two percentage points higher than Mr. Mondale's - fits into defense and budget needs.
The two men differ on the mix of weapons and have different attitudes about the military in relation to foreign policy. Reagan stresses weapons systems; Mondale, diplomacy. Mondale would eliminate big-ticket items (the MX missile, the B-1 bomber, the ''star wars'' defense program) and upgrade readiness. Reagan favors the big-ticket items. The B-1 program alone will cost taxpayers some $28 billion. But given the sheer magnitude of the deficits - which in themselves are a very real danger to the nation's long-range economic well-being - some tough choices have to be made.