Washington — Why were the Russians so sensitive to the prospect of anti-Soviet activity by emigre groups at the Olympic Games? A State Department official offered an explanation:
''We'd be sensitive, too, if, instead of half a million Indians in the United States, we had 50 million Indians and all the various groups wanted independence.''
And - the official might have added - if the Indians had fellow tribesmen in the Soviet Union who supported their cause.
Diplomatic and academic experts do not believe that planned agitation by ''extremist organizations'' in the US - gathered under the umbrella group called Ban the Soviets Coalition - was the sole or even dominant reason for the Soviet pullout from the Olympics. But they do not discount it, for it touched on that historical and political raw nerve known as the ''nationalities question.''
The point made is that the Union of Soviet Socialist Republics is an empire. Most of its territory, even the Russian heartland, is comprised of numerous nationalities, many of which were once independent or quasi-independent nations or aspire to be so. The Ukraine has been independent for brief periods. Armenia and Georgia were once independent. The old Central Asian khanates, while not having the attributes of nation-states, ran their own affairs.
In short, the Russian and then Soviet state has been expanding for centuries and virtually all the areas around the periphery had some kind of previous political existence. Furthermore, as the Russians and Soviets moved outward, they absorbed people who often were at a higher political, economic, and social development, a fact that contributes to their own cultural insecurity.
The Baltic states are a case in point. Independent between the two world wars, the more advanced nations of Lithuania, Latvia, and Estonia were occupied by the Soviet Army in 1940. After so-called ''elections,'' they were absorbed into the USSR.
Adding to Soviet sensitivity is the fact that the United States to this day has not recognized the forcible incorporation of these Baltic countries. Surprising as it may be to many Americans, the original legations of independent Lithuania and Latvia still function in Washington, and Estonia has a consulate-general in New York. A State Department desk officer maintains regular contact with the three legations, which are dealt with in the department under the European, not the Soviet, bureau.
Each year, moreover, the President of the United States, under a congressional resolution, proclaims Captive Nations Week to focus national attention on the plight not only of the Baltic peoples but of the Ukrainians, the Armenians, the Poles, and a host of other nations that have fallen under communist sway.
Although the Soviets claim they have no ''nationalities'' problem, that the Soviet Union today is one happy family of diverse peoples and ethnic groups - all looking to the dominant Russians for leadership - the reality is far different. Ever since the Bolshevik Revolution, when Ukrainians and other nationality groups took up arms in an effort to crush the Bolsheviks and gain independence, the Soviets have had to face the problem of ethnic nationalism.
Ukrainians have openly resisted cultural Russification. The Lithuanians, Latvians, and Estonians, resentful of the Russian presence, resist speaking Russian and look for ways to enhance their own national identity. The Uzbeks and other groups in Central Asia cling to their own ways and customs. From among various ethnic groups - Crimean Tatars, Jews, Ukrainians - also come many of the political dissidents who, though a decided minority, are a constant thorn to Soviet authorities.
Most experts view ethnic nationalism as the most troublesome problem for the Soviet leadership over the long term. It goes to the heart of Kremlin reluctance to decentralize economic power. Once economic controls are loosened at the center, political control grows more difficult. In time, centrifugal nationalist forces could pull the Soviet empire apart.
This is an outcome many former citizens of Eastern Europe now living in the US desire and actively work for. ''After the next big war, Estonia will be free again and Russia will be divided just as Germany and Korea are,'' says an Estonian-American.
So Moscow took quick notice when the Ban the Soviets Coalition was formed in California to demonstrate against the Soviets at the Olympic Games and to encourage and assist Soviet defectors. In American eyes, the group posed no real threat to Soviet personnel.''It was just a little group until the Soviets made it a big deal,'' says one US official. But it loomed as a worry nonetheless.
''The Soviets are afraid of losing defectors to the free West,'' says Aristide Nicolaie, a member of the Captive Nations Action Committee. ''They've had a lot of defections - artists, ballet performers, and others. Before, there was practically no organization to work on this. But now that an organization has been set up and gathered funds for this purpose - to support defections - this is a serious problem for them.''
The coalition embraced 165 organizations from across the nation, including such ethnic, political, and religious groups as the Baltic American Freedom League, Polish American Congress, American Conservative Union, Young Republican Federation, Church League of America, Council of Korean Churches, and Christian Voice Lobby. A variety of activities - from billboards and aerial banners to demonstrations and facilities for defectors - had been planned with the participation of about 15,000 people, say the coalition organizers.
''We anticipated about 200 defections from the entire Eastern bloc,'' says David W. Balsiger, founder and director of the coalition. ''Most would not have been athletes but security personnel, journalists, technicians.''
Now that the Soviets are not coming to Los Angeles, the leaders of the coalition hope to perpetuate the organization. ''The name change is a problem, but in the future we'd be an ongoing organization to focus on human rights violations and to aid defectors anywhere in the world,'' says Mr. Balsiger, an executive with a high-tech advertising agency.
Not all Americans of East European background and strong anti-Soviet persuasion wanted a Soviet walkout. ''The coalition made too much noise too early,'' remarks one former East European. ''They should have let the sportsmen come and then cry 'wolf.' ''
But many others are pleased with the way things turned out. ''I have no regrets,'' says Viivi Piirisild, secretary of the Baltic American Freedom League. ''I feel bad because there were Baltic athletes that could come and could have competed.But the Soviets were not in the Olympics before 1956 and I see no reason to have them.''
''The Russians hate the Baltic League because our movement has helped influence world opinion,'' adds Mrs. Piirisild. ''The dissident movement in the Soviet Union sooner or later has to explode. So there is reason to help keep it alive, because there are so many violations of human rights in the Baltic countries.''
Heightening Soviet concern is the fact that President Reagan has displayed somewhat more attentiveness to such groups than previous American leaders. Last year he invited 250 Baltic-Americans to the White House on Baltic Freedom Day. The State Department now singles out the Baltic states in its annual human rights report. And last month US Assistant Secretary of State for Human Rights Elliott Abrams addressed the Baltic congress on the West Coast.
American officials are careful to point out, however, that while the US upholds the right of free speech and may be sympathetic to such groups, it is not on a crusade to ''free the captive nations.'' Nor has there been any shift in US policy.
''This administration takes a strong stand in favor of self-determination,'' says one official, ''but it doesn't mean we support independence movements or recognize the Ukraine.''
In recent years, the Soviets have grown more sophisticated in their handling of emigre groups. They have developed a vast apparatus to try to get them to be , if not pro-Soviet, at least not anti-Soviet. Books and magazines are published in almost all the USSR's major languages. And emigres and their US-born children are encouraged to visit the USSR.
At the same time, the Soviets have an almost paranoid reaction to organized anti-Soviet emigre activity in the US, especially when they think it is supported in the White House.
''Every time you talk about the rights of the Baltic nations you step on a sore toe,'' says a State Department analyst. ''They cannot ignore it. If you're a Soviet, you're convinced that the President is out to get you through your 'soft underbelly.' ''