No one can say for sure where the Soviet Union is headed after the nation's Communist Party ended a rare conference this past week. The 5,000 delegates heard unprecedented arguments over such formerly taboo issues as a freer press, the "mistake" of Afghanistan, religious rights, the economy, more elections and elections by secret ballot, limits on terms of office, and many others.

The debate was often sharp, and whether Soviet leader Mikhail Gorbachev can carry out his program is still an open question. The conference closed with no clear indication as to the fate of many of his reforms.Perhaps the best clue will come from what happens in coming months to two individuals - Soviet President Andrei Gromyko, who was foreign minister for 28 years, and Vladimir I. Melnikov, a local party boss in the region of Komi.

During the conference, Melnikov addressed the delegates and said the Soviets want high officials who served under Brezhnev - the target of much criticism - removed from office. When asked for specific names, Melnikov mentioned two people, one of them, Gromyko. "Comrade Gromyko has fallen behind the times," he declared.

In years past, such open criticism of a major figure by a minor official would have been greeted with stunned silence. This time, the delegates actually applauded.

However, next day, the 78-year-old Gromyko was honored with the chairmanship of one of the closing sessions. He was shown on public television standing at the lectern, conducting the meeting.

If Gromyko remains in public positions and Melnikov vanishes into Siberia, it will be a demonstration of the lack of substance behind "glasnost." But if Melnikov stays and Gromyko goes - well, almost anything might become possible in Russia.