THE crisis in the Chechen-Ingush autonomous republic, a tiny region on the northern slopes of the Caucasus, marks the beginning of a series of events that may result in a final destruction of the central Soviet government and the emergence of a purely Russian army and a more authoritarian government in Russia.Although temporarily eased by the unwillingness of the Russian parliament to enforce the state of emergency declared by President Boris Yeltsin, this crisis could evolve into a civil war of unknown scope and duration that would ultimately pit - as many times before - the Russian Christians against the Muslims living in the southeastern provinces of Russia. If it came to a fight, Russian interior ministry troops might be able to quell the supporters of Chechen nationalistic "President" Dzakhar Dudayev, whose legitimacy is questioned by Moscow but who has vowed to fight Russia by all possible means. But another, more serious threat looms in the East, in the vast basin of the River Volga, populated by numerous non-Slavic peoples that also seem to be gripped by an independence fever. And the interior ministry troops may not be strong enough to cope with it. In Tatarstan, an autonomous republic sandwiched between the central Russian plains and the Ural mountains, the crisis is potentially more deadly than in Chechen-Ingush. The republic has proclaimed its independence and seeks to assert it in any way it can. The Russian government decrees are being ignored. Buoyed by Moscow's weakness and preoccupation with other problems, Tatar nationalists are already presenting claims on Russian territory. They hope to link their republic to Kazakhstan, which has a substantial Muslim community, and thus strengthen the Islamic influence in the southeastern part of Russia. "These territories are ours," Fauzia Bairamova, the nationalist leader in the Tatar parliament states bluntly, referring to lands that lay to the south of Tatarstan. These nationalist movements together create a dangerous stretch of instability along the basin of the Volga, a region rich in oil, gas, and other resources and, therefore, vital to Russia. There is no chance Moscow will be as tolerant with them as it has been toward secessionist union republics. Under no circumstances will Russians, who have loathed Tatars since the Middle Ages, accept the breakup of their country, much less the resurrection of the Golden Orda, an expansionist medieval Tatar state, in their backyard. HOWEVER, the nationalists in the Volga region may have already gone too far to be swayed by reason. Russia's only practical option may be to "pacify" them militarily. One condition has to be met, however, before Mr. Yeltsin could deal the nationalists a decisive blow: He has to have an armed force under his full control. Moreover, this force would have to be free of servicemen that do not share Russian interests and aspirations. This wouldn't be an easy task to achieve. So far, the Soviet Army has been a melting pot of all nationalities, with ethnic conflicts brewing inside but rarely spilling into the open. It made the Soviet Army reliable enough for invading foreign lands but hardly fit for calming restive minorities inside the USSR. Demographic trends for the last 20 years have complicated the problem. While the population growth in the Slavic republics virtually came to a halt, it continued steadily in Central Asia, increasing the share of Muslim conscripts drafted every six months into the armed forces. It has been calculated that if these demographic trends continue and the system of recruitment remains the same, the Soviet Army may become a 40-percent Muslim force by the year 2015. Already up to 30 percent of new recruits in som e units do not speak any Russian, statistics show. Such an ethnically diverse force obviously cannot be used by Russia to reassert its authority in Tatarstan and other hot spots. Kazakhs, Uzbeks, and even Ukrainians now in the armed forces cannot be counted on as partners in Russian internal military campaigns. Therefore, to remain in control, Yeltsin will need - and fairly soon - an essentially Russian army under his uncontested command. It would spell dissolution of the Soviet Defense Ministry, one of the last strongholds of Soviet President Mikhail Gorbachev, and the division of its assets between the newly independent union republics. It may explain why the independence-minded Ukraine was reported to have easily concluded in November an agreement with Russia on dividing the armed forces. If these reports are true, the Russian government could have been motivated only by one imperative: its own urgent need to set up a reliable force to stabilize the rebellious provinces in the East. Before becoming leader of the Chechen-Ingush nationalists, Dzakar Dudayev flew a strategic bomber for the Soviet Air Force. While patrolling the skies in the vicinity of the NATO countries, he may have dreamed of driving the Russians from his native land and joining the Islamic world. It is good that now, with Chechen-Russian hostilities erupting, he's far away from his bomber and its deadly nuclear weapons. But how many others like him - Tatars, Ingush, Armenians - still serve in the ranks of the so-called "Soviet Army," handling weapons for a state that is no more while feeling other loyalties? This is the question that President Bush and other NATO leaders, who recently issued a declaration in support of President Gorbachev and a unified Soviet military, have to ponder.