Soviet foreign policy - how far can the bear's paw reach?

The Reagan administration, now in its 14th month in Washington, continues to operate on the assumption that the Soviet Union is an expanding world power that can be checked only by a massive increase in American military power and by the use of it in places like El Salvador.

This week it is trying to persuade Congress to let it send more guns to El Salvador to try to check presumed Soviet expansionism there through Nicaragua.

But just how successfully expansionist is that Soviet state?

The latest news from Afghanistan is that the Soviets have increased their troop strength in that country from some 80,000 men up to 100,000. They are said to have had a recent success in an operation north of Kabul. But they are in the 27th month of their military occupation. Resistance continues to be widespread and bitter throughout the country.

The Soviets have not had a brilliant success in Afghanistan nor, in terms of power politics, an adequate return on their investment in lives and treasure. They have not yet paid as high a price as the United States did in Vietnam, but they do not yet see light at the end of their Afghan tunnel. After 26 months of fighting Afghanistan continues to be a drain on Soviet military and economic resources.

They have had a success in Poland. Effective Soviet control through the agency of the Polish Army has been reestablished at the top. Superficially at least Moscow has restabilized the situation in Eastern Europe.

But there has been a price. The desire of the mass of the Polish people for release from Soviet control has been underlined and advertised by the Polish crisis. The use of force to suppress them has weakened the value of the Polish Army in the Warsaw Pact order of battle.

The willingness to use force shocked the outside world and undermined Soviet diplomacy and Communist Party influence in much of the world. The suppression of freedom in Poland goes down as an expensive defensive success for Moscow, but the costs include the necessity now of bolstering the Polish economy.

Perhaps the Kremlin lists some compensation from the impact on Western Europe of Reagan rhetoric and operations. Neutralism and antinuclear demonstrations have risen to plague such prominent NATO leaders as Chancellor Helmut Schmidt in West Germany. His chances for reelection have been damaged by his commitment to the deployment of new US nuclear missiles in his country.

But any gain for Soviet influence in Western Europe has come not from things Moscow has said or done, but rather from things said and done in Washington. Reagan emphasis on weaponry has tended to frighten or alienate Europeans. Reagan policy toward Central America is unpopular and unpersuasive among the NATO allies.

Kremlin opportunities have improved of late in the Middle East, but again not from positive things said or done by Moscow. Reagan failure to reconcile Israel and the Arabs has ruined the concept of a ''strategic consensus'' in the Middle East uniting Israel and the Arabs. During the past week Mr. Reagan's special Middle East negotiator, Philip C. Habib, was again in the area doing his best to dissuade the Israelis from invading Lebanon and/or Syria. The more Arab-Israeli trouble, the better the opportunities for Soviet intervention.

The same, of course, holds true in Central America. The more Washington offers guns to right-wing governments or dictatorships, the more the opposition movements look toward Moscow for counterbalancing support.

But there have been no fresh Moscow ventures launched since the Afghan invasion. Earlier ones continue to be expensive. Moscow has to underwrite much of the cost of the Vietnamese attempt to stamp out independence in Kampuchea (Cambodia). China continues to support resistance among some small Kampuchean independence forces. Pol Pot still seems to operate in hill regions near the Chinese border.

Economists begin to wonder how long the Sovet economy can stand the drain on it from the unfinished wars in Afghanistan and Kampuchea when it must also help sustain the economies of Angola, Mozambique, Ethiopia, Vietnam, and Cuba.

And if Mr. Reagan is correct about the aid going to the rebels in El Salvador and to the revolutionary government in Nicaragua, then Moscow is shouldering further costs. West German Foreign Minister Hans-Dietrich Genscher says:

''I think there can be no doubt that the international commitments of the Soviet Union extend far beyond their capability of economic assistance.''

The highlight of the past week in Washington was the release and publication of aerial photographs showing the military buildup over the past year in Nicaragua. According to CIA briefing officers, the photographs show that Nicaragua now has armed forces of approximately 70,000 men which are armed by 25 Soviet tanks of the T54/55 generation. Cuba has 200 such tanks in its arsenal. It is a tank the Soviets provide to their satellite and dependent clients.

The photographs also purportedly show airfields with MIG-17 Soviet planes and the capability of taking MIG-21s, a later and better military aircraft. The Cubans have about 80 MIG-21s.

The implication is clear that Cuba has been handing on to Nicaragua some of the military largesse it has long been enjoying from Moscow. There have been indications that the Soviets have recently shipped new and better weapons to Cuba, thus permitting the Cubans to pass along some of their older equipment to Nicaragua. The Nicaraguans claim they are threatened by invasion from the US by Nicaraguan right-wing refugees training, with US government consent, in Florida and California.

President Reagan continued over the past week to insist that his entire defense budget increases are necessary to sustain a policy of containing Soviet expansion. But there is increasing doubt in the Congress that quite so many guns of so many different varieties are necessary when the Soviets may be overextended and in deep economic trouble.

Also Kremlin watchers are excited about a number of signs of political unrest in the Soviet leadership. Some believe that the passing of Mikhail Suslov, long the party's custodian of orthodoxy, has upset the political balance inside the leadership and that a struggle over the ultimate succession to Leonid Brezhnev has begun. A scandal involving top figures in the famous Moscow circus has involved Brezhnev's daughter, Galina Churbanova.

Much current world news adds up to a possible rationalization for cutting back on the Reagan defense budget. If Moscow is, indeed, in so much trouble as many signs indicate, then must Mr. Reagan risk economic bankruptcy to get so many new weapons so quickly?

The question has not yet been reported from inside the White House. But it is widely being asked in Congress and in other US political circles.