THE PROPOSAL to open up large-scale youth exchanges between the U.S.A. and the U.S.S.R. was, according to President Reagan, "one of the most exciting achievements" of the Geneva Summit. Addressing a joint session of Congress on his return from Geneva Nov. 21, Reagan affirmed that people-to-people exchanges "will help break down stereotypes, build friendships and, finally, promote an alternative to propaganda."

Skeptics have rightly pointed out that the Soviets are unlikely to permit thousands of their most impressionable young people to gain firsthand exposure to American life. But not all the impediments are on the Soviet side. If a large-scale program of exchanges of high-school-aged youths were opened tomorrow, Americans would be unable to participate. The reason? To few young Americans are able to communicate in the Russian language.

The most recent data from the schools makes this deficiency abundantly clear. Only one out of five American high school students is studying any foreign language today as contrasted to five out of five in the U.S.S.R. Those Americans studying Russian number a mere 5,702 from coast to coast.

In each of 32 states, fewer than 50 students are learning the Russian language at any level today. In spite of the importance of the U.S.S.R. in our lives, seven times more American school children study Italian than Russian, the number of Latin students is 32 times greater, and of those learning French fully 150 times larger.

It takes several years of study to gain a solid foothold in Russian. Yet among all young Americans in grades seven through 12 only 1,136 were above the second-year level in 1983, the most recent year for which complete data is available. In other words, only a few hundred high school students in the entire country have any practical competence in Russian.

Didn't Sputnik change all this, one might ask? Not really, for the post-Sputnik boom was both limited and brief. Even in the peak year of 1965, only 35,000 American high school students were studying Russian. By 1985 the number had plummeted to a seventh of that.

Surely, though, the situation is better in the colleges and universities? Not really. In 1983 only 30,000 American college students were studying Russian. A much-touted "recovery" since then has been, in actuality, very limited. At present rates it will take a decade and a half to catch up even to the level of the late '60s.

Even if that humble goal were attained, it would leave Russian language studies lagging far behind French, Spanish, and German in U.S. colleges. Moreover, only a handful of college students of Russian persist beyond the introductory courses. Like their counterparts in high school, most college students of Russian get all of the agony and none of the usable rewards.

It is all but impossible to participate in meaningful cultural exchanges without knowledge of the other side's language. Language, after all, is at the heart of culture. Soviet youths are at a disadvantage in that their government prevents them from traveling freely in the United States. Nonetheless, millions of them study English.

Our young people are at an even greater disadvantage because, for all their freedom to travel, they lack the essential linguistic skills to participate in intercultural contact. The fault is not their own. It is due, rather, to the failure of American educators in colleges, universities, and especially in secondary schools to provide the opportunity and encouragement for Russian language study.

The U.S. is the only industrialized country without a universal foreign language requirement in its high schools, and the only one that would allow its population to remain almost wholly ignorant of the language in which its chief adversary thinks.

Can the situation be improved? Possibly, but only if some mistakes from the past are corrected. First, it is impossible to build a corps of Americans fluent in Russian by starting at the college level. The attempt to do so has failed over 20 years, and for an obvious reason: College is too late. The center of language teaching must be in the schools -- high school if necessary, but preferably the middle schools or even grade schools. To start later is like trying to build a house from the roof down.

Second, no progress will be made until we back the classroom teachers of Russian (and of foreign languages generally). Few state school boards or teachers' colleges value fluency in a foreign language and the ability to teach it. As a result, many of those who know Russian best -- including recent immigrants from the USSR -- cannot easily become certified to teach, while those with the necessary certification all too often lack the requisite fluency.

Without a larger group of Russian language teachers, President Reagan's dream can never become a reality.

There is a simple solution to this teacher shortage. Let's send a few hundred prospective teachers of the Russian language to the USSR to polish their fluency and build their pedagogical skills. They can make themselves useful by teaching American English in Soviet classrooms.

Meanwhile, let's open up a hundred or more positions in American classrooms for Soviet exchange teachers who can teach Russian for a couple of years each. While they do so, they can sharpen up their English for later use in classrooms back home.

Through such an effort, we would be in a position three years from now to send large numbers of well- prepared American high school students to participate in exchanges in the USSR. Meanwhile, those in each country most immediately involved with introducing the other country's culture and values to young people -- the language teachers -- would approach their task with a degree of knowledge commensurate with their responsibilities. Only in this way will cultural exhanges live up to the high expectations of the Geneva summit.