People talk "war and peace" as if the issue were entirely up to the United States. But Russia also plays a major part. So before judging the candidates, it makes sense to assess the present Soviet stance in the world.

Moscow has recently shown new signs of firmness. Particularly revealing is the dramatic public reception the Russians accorded to the visiting puppet leader from Afghanistan, Babrak Karmal. President Leonid Brezhnev embraced him at the airport and said at a dinner in his honor that the Afghan revolution was "irreversible." That means the Russians are sticking firm by their commitment in Kabul, cost what it may. It will be four or five years, Russians here freely admit, before Soviet troops are out.

The Russians show equal determination not to let the unrest that recently swept Poland spread there or to the rest of Eastern Europe. In the last few days they have allowed the East Germans to tighten the rules of contact with West Germany. Moscow thus announces a willingness to crack down hard -- even at the expense of harmony with Western Europe.

Then there is the Soviet behavior in the Persian Gulf crisis. Moscow is simply allowing assets to accrue -- firming up ties with Iraq by arms shipments, with Syria by a new security treaty, with Iran by encouraging clients such as Libya to help Tehran. Whatever happens in the Gulf, the Russians will be in good position to pick up some pieces.

Within that context, the Russians continue to negotiate with the United States on arms control. In other words, with their vulnerable positions secured and the way open for new advances in the Persian Gulf, they are also prepared to move forward with the arms limitation treaty known as SALT II.

Jimmy Carter's Russian policy centers on passage of the SALT II treaty. He also proposes a modest defense bill, centering around a new missile, the MX, and a Rapid Deployment Force. He would put further pressure on the Russians by firming up ties with China, by pushing hard on human rights and by courting the Third World countries, including the radical regimes.

But with the Russians toughing it out, Carter has no chance for early Senate ratification of SALT II. Indeed, he has hurt the cause by bringing the treaty front and center as a partisan -- almost personal -- political issue. In the process he may even have compromised the credibility of his most weighty witness -- Defense Secretary Harold Brown.

Neither can Carter hold the line on defense spending. His emphasis on the China connection and on human rights panics the Russians into a steadily increasing arms buildup. The buildup combines with successes scored by radical regimes in Asia, Africa and Latin America to fortify hawks in the Pentagon and Congress. Thus Carter's good intentions work now, as they have during the past four years, to fuel the arms race. His policy remains the prisoner of his self-righteousness.

Reagan approaches the Soviet Union all growls. He would scrap the SALT II treaty. He favors a much bigger defense buildup. He leaves it open as to whether he would use force in the Persian Gulf or the Caribbean. He claims that under such pressures the Russians would quickly accede to a new and much better arms control accord -- SALT III.

But hardly anybody believes the Russians would yield to such pressures. On the contrary, the scrapping of SALT II would free them to accelerate the military buildup. They know Reagan commands almost no domestic support for military adventures or for big defense spending. They would be further emboldened because Reagan shows no interest in working with China against the Soviet Union.

So the Reagan line, while sounding tough, actually provides new openings for Soviet expansion. Much as Carter is trapped by his moralism, Reagan is the captive of his outworn ideology.

In the matter of national security, accordingly, neither major candidate offers assurance for the years ahead. The one least committed to his present posture is probably -- if not the best -- the least bad.