RESTRUCTURING has its limits. That's what the Soviet leadership seemed to be saying in stridently rejecting pleas to unite the autonomous region of Nagorno-Karabakh with the socialist republic of Armenia. Months ago, when the controversy was starting to simmer, Mikhail Gorbachev had indicated he might be willing to take a more conciliatory approach. He met with activists who laid out their case for making the predominantly Armenian region part of Armenia proper. Since 1923 Nagorno-Karabakh has been administered by the largely Muslim republic of Azerbaijan.
Armenian hopes were raised. Demonstrations were launched, strikes organized, and at one point lives lost as Armenians and Azerbaijanis clashed in the Azerbaijani city of Sumgait.
Confronted with this outburst of popular, nationalistic feeling, the attitude of Soviet officialdom hardened. The problem had Mr. Gorbachev over a barrel. His policy of openness had spawned the attempt to air and adjust what Armenians viewed as a long-building grievance. Yet this grievance raises an issue that goes to the heart of Soviet governance: the nationalities question.
Nationalistic aspirations bubble all over the Soviet landscape: Armenia, the Crimea, the Baltic states, the Ukraine. Faced with the prospect of setting a precedent by recognizing one set of these aspirations, the Politburo and Gorbachev did the obvious: They squelched the idea in terms that clearly indicated that this kind of thing would not be tolerated.
For the Soviet leader and his colleagues, Nagorno-Karabakh may have provided training under fire. The present Politburo has only one non-Russian member. No one in the ruling group around Gorbachev has served in the non-Russian republics. Gorbachev himself had never given a speech on the nationalities issue before his address on the Armenian-Azerbaijani dispute.
The leadership's firm declaration that borders in the Caucasus region will remain unchanged may put the Armenian question to rest for the moment. But demonstrations and strikes may continue in Yerevan, Armenia's capital, and elsewhere. Ethnic feelings are running high.
To the north, Soviet citizens in Estonia and the other Baltic republics are forming national front organizations that come close to being competing political parties - and doing so in the name of perestroika and Gorbachev, whom one Estonian has described as ``our angel.''
The present outcome in Armenia indicates that Gorbachev may be less than angelic if pushed too far on the nationalities issue. His policy of restructuring and liberalization never really took into account the Soviet Union's ethnic and national diversity - a diversity that can be seen as demanding tight central control. Events may now force him to correct that oversight, but the task won't be easy.