The turf on which tonight's debate will be played will most likely be a variant of what might be called Reagan's Question: Are you better off today than you were four year ago? For purposes of foreign and defense policy, the variant is: Is the country stronger and more secure than it was four years ago?

Because it's a question involving a comparison, to answer it you need to determine not only how safe and secure we are today, but also how safe and secure we were four years ago. President Reagan will say we were perilously weak -- a paper tiger militarily after a "decade of neglect" and consigned diplomatically (not by coincidence!) to watching helplessly as the Soviet Union added to the string of its puppet states.

Oddly, it isn't an important part of Walter Mondale's foreign policy pitch to dispute this point. He in effect concedes that we're stronger, but he argues that that hasn't made us more secure because of the dangers -- nuclear proliferation, our chilly relations with the Soviets -- that come with a hard- line policy. So Reagan has the picture of a nation that was on the ropes when he took office all to himself.

But is it really true? At the very least, it's a notion that somebody ought to dispute, and not just on grounds of setting the record straight. Especially in foreign policy, perceptions are important because they quickly become the basis for actions. The perception of crisis in 1980 certainly did -- its result was the unprecedented increases we've had in defense spending. A more fruitful line of criticism of Reagan on foreign policy than the one Mondale uses might be that because the perception was wrong, the actions were too, with harmful consequences.

We pulled out of a war in the early 1970s -- under Republican presidents -- and, as has been the case every other time a war ended, our defense budget went down for a few years, relative to inflation. The Republicans also replaced the draft with the All Volunteer Force, after which -- in the 1970s -- the quality of the enlisted ranks began a sharp decline.

Jimmy Carter was elected president on the standard Democratic pledge to cut defense spending, but in fact it rose while he was in office, partly because he became more hawkish. The foundation on which his reputation as a weak commander in chief rests is probably the hostage crisis, which had nothing.

Reagan, though, did best against Gerald Ford in 1976 when he was at his most hawkish, and he continued to push that theme in against Carter. If you'll remember, he ran on the pledge of a $200-billion budget for national defense.

In 1980 Sens. Sam Nunn and John Warner sponsored a bill raising military pay, which had the effect of starting a dramatic turnaround of the military's personnel problems -- before Reagan took office. Then, after losing the election, Carter decided to fiddle with the bargained-out numbers in his final defense budget. He made them public five days before leaving office, and by some strange coincidence, the number he proposed for national defense was $200.3 billion.

This left the new Reagan administration in the position of having to one-up the appeasers, even though Reagan's campaign promise was already being met. So before two weeks in office had passed, Caspar Weinberger, a defense neophyte, had picked the number of $32.6 billion by which to increase defense spending -- and that was on top of the huge increase that Carter had already proposed.

To spend that much that fast, you have no chance to come up with a real strategy; the money went mostly to another big pay raise and to increased orders of the weapons systems that were already around. For example, Weinberger has recently effectively killed the Sergeant York division air defense gun as a turkey, but back in 1981 he was upping production of it in the name of "rearming America."

Ever since, it has been established that defense budgeting arguments will be over real percentage increases far greater than the five percent that Reagan campaigned on in 1980. Meanwhile, the military arguments about American weakness -- weapons that don't work well, areas where the Soviets are ahead of us, vulnerabilities in our nuclear forces, horror stories about ammunition and spare parts -- can virtually all be made in exactly the same terms as they were four years ago.

But it is still put forth that the Soviet march during the Carter administration has now been stopped, in large part because of higher defense spending. "From the fall of Saigon in 1975 until January 1981," Jeane Kirkpatrick said at the Republican convention, "Soviet influence expanded dramatically into Laos, Cambodia, Afghanistan, Angola, Ethiopia, Mozambique, South Yemen, Libya, Syria, Aden, Congo, Madagascar, Seychelles, Nicaragua, and Grenada." Quite a bit of this expansion, though, took place during Ford's term (in Laos, Cambodia and Angola, for example), and in most of the other countries (Nicaragua being the classic case) the Republicans' real quarrel with our policy is diplomatic, not military.

One day, God forbid, we may find ourselves in a real military crisis. If that happened, it would be a tragedy if we had to respond with a military grown fat and sluggish from being given war-time budgets during peacetime, and a public become balky after too many cries of wolf from Washington.