As they celebrate the 60th anniversary of the Bolshevik Revolution this week, the leaders of the Soviet Union cut a curious figure. They present no serious immediate challenge anywhere in the world.

Except for moving apart in arms control. Russia and the United States are resisting manifold openings for making trouble at each other's expense. There is in effect a kind of undeclared detente.

The most instructive example of what is happening, though not the most important, occurs in the Indian subcontinent. Sweeping changes involving the ouster of idolized leaders have recently taken place in India, Pakistan, Bangladesh and Sri Lanka. In the past the Big Two would have been fishing like crazy in the troubled waters.

But now the domestic politics of South Asia are domestic politics. This time both Russia and the United States have kept hands off.

Similarly in Western Europe. A threat to political stability there was posed in the bid of Communist parties to come to power by moderating their dependence on Moscow and underlining nationalist appeals - the program known as "Eurocommunism."

The chief testing ground for that approach - the pacesetter for Italy, Spain and Portugal - has been France, where the Communists, joined in a front with the Socialists, looked to be in strong position to win the parliamentary elections in March. But the French Communists have not been prepared to go along with the Socialists at any price. They have precipitated a split about nationalization of industry by the future government. The fight has caused a rift between the Socialist leadership and the Communists, and all evidence suggests that the split will probably cost the left wing the election.

Moscow's role in these developments was probably not decisive. But clearly the Russians weren't happy about the alliance of a revisionist French party with the Socialists and are now rejoicing in the split. In practice, in other words, the Russians prefer economic and diplomatic cooperation with a right-center French government to the headache of dealing with a weak and divided France under left-wing rule.

Africa offers still a third case in point. The Big Two initiated their present cooperation by joint action to prevent the Republic of South Africa from developing nuclear weapons.

The Russians have increased their influence in Angola, where they helped a rebellious faction to power, and in Ethiopia where they supplied arms to a regime hard-pressed by separatist guerrilla movements. But in Angola the Russians and their proteges have fallen out. Russian support for the regime in Addis Ababa cost Moscow a privileged position in Somalia, which is backing the separatists against Ethiopia. The Russian "gains" have been more trouble than they were worth, and the United States is wisely standing by letting Moscow sweat out three bits of nowin diplomacy.

The Middle East is a far more dangerous area. But the Russians and Americans did issue a joint set of principles for convening the Geneva conference. The Russians may not be doing much to bring the Syrians and Palestinians to the conference. But they are not making matters worse by stirring up new demands. Clearly the Russians would like to go to Geneva, and as long as there is movement toward or at Geneva, war is not on.

Finally, of course, there are the joint efforts being made by Russia and the United States in arms control. New possibilities for a complete test-ban treaty have been opened by the speech of Party Secretary Leonid Brezhnev last week. It still looks as though the general guidelines for a new strategic-arms treaty, worked out in Washington by the President and Foreign Minister Andrei Gromyko last September, will bear fruit. The agreement shaping up is not perfect and is far worse than what the Carter administration sought in Moscow last March. But if only because it means that further talks will continue, it is far better than having no agreement.

I do not for one minute believe that the Russians have suddenly become a benign force in the world. Perhaps the present lull only means that they are building up their military might with Western technology. Maybe they are more concerned about China that about the United States. Perhaps it is just a case of Brezhnev, as he nears the end of his career, retrieving what he can out of detente.

Moreover, an unfree society continues with undoubted presecution of dissidents, so at best the United States and Russia will have a complicated relationship, mixing bits of cooperation with bits of competition. But clearly it makes sense to expand the cooperation, to multiply ties with the Russians, and if possible to behave in a way that enables Brezhnev to turn over the leadership to another man with the same commitment to detente.