You haven't heard the last of the Ronald Reagan-Taiwan issue.

Reagan was left with a sticky problem by the Carter administration: Should the United States sell new fighter planes to Taiwan and, if so, which ones? A decision must be reached soon. Whichever planes may be offered, the mainland Chinese will object vehemently.

Two entries are in the field: Northrup's souped-up Freedom Fighter and General Dynamics' watered-down F-16.

The F-5E Freedom Fighter is due to go out of production in 1983, and Northrup hopes to bring out a new, more powerful version after that. General Dynamics proposes to remodel the much more sophisticated and expensive F-16 to make it less complicated and more appropriate for developing countries.

Some US policymakers think the Freedom Fighter will seem less threatening to Peking than the F-16.An order of 300 planes hangs in the balance.m