WHAT WILL happen to 14-year-old Walter Polovchak now that an Illinois court has decided he should not have been removed from the custody of his parents? Immigrants from the Soviet Union, they had sought unsuccessfully to take him along when they returned to their native Ukraine last year.

The youngster, who chose then to remain in Chicago, was removed from their custody and made a ward of the state. It was this action that the Illinois court reversed this week, holding that the normal conditions for removing a child from parental custody were not present in this case. Most family law experts would agree.

The state court, however, could not and did not reach the more fundamental question of whether Walter could be forced to return to the Soviet Union against his will. The U.S. government has granted Walter "religious asylum" on the grounds that, as a Baptist, he would be subject to persecution in the Soviet Union. The Illinois ACLU, representing the parents, maintains that the government should not have made this decision without consulting the parents. The ACLU will argue in federal court that since custody has been restored to the parents, they should be allowed to retrieve their son, even if he does not consent. The Justice Department finds the custody issue immaterial and will fight any such effort.

It has been difficult to reach the Polovchaks with news of their victory in the state courts, so it isn't known whether they will come for Walter or ask that he be sent to them. Perhaps they are resigned now to having lost him and will not reopen a painful wound by forcing the recalcitrant teen-ager to return. Perhaps they are under pressure from their own government to pursue this case. Their predicament as human beings caught up in an international tug-of-war deserves sympathy.

As for Walter, the Illinois courts have settled the domestic relations question. But the political question --under what circumstances can asylum be sought and granted?--will probably be settled by the inexorable march of time. Walter was 12 when he first left his parents' home. He is 14 today. On the question of whether he can leave, the decision--at any age--is his alone. On the question of whether he can stay against his parents' will, the federal court is moving slowly. It's quite possible he'll have grown a mustache before all the appeals are decided. If he hasn't changed his own mind by then, chances are he'll be buying his razor blades in Chicago.