Federal prosecutors yesterday indicted a West German businessman living in Falls Church and three other Europeans on charges of illegally exporting controlled electronic components to Austria.

The U.S. Attorney's office in Alexandria, in a 20-count indictment, alleged that Gunther R. Nachtrab purchased and exported microwave circulators, telling U.S. authorities they were destined for the communications system of the West German postal service.

However, the components, shipped to a company in West Germany, were sent on from there to Austria, the indictment says. Prosectors say the parts' ultimate destination was a Soviet bloc country.

Reached by telephone at his company, Text Editing Equipment of Falls Church, Nachtrab said he had not seen the indictment and declined to comment.

The indictments, which grew from a year-long investigation in Washington and Western Europe, come as President Reagan is asking Congress to strengthen the Export Control Act, which governs export of high-technology goods.

Assistant U.S. Attorney Thomas M. Buchanan said the investigation into Nachtrab's dealings began in March 1982 after two of his employes approached authorities and told them that goods were being exported without proper papers and that dollar amounts on invoices were being understated to avoid paperwork required for large shipments.

According to the indictment, Nachtrab went to Vienna, Austria in November 1981 and discussed export of high-tech goods to Soviet bloc counties with two of the other defendants, Anna Landau and Jeanette Wellems, both of Steuerungstechnik Und Messgeraete, an export-import company there.

Wellems instructed Nachtrab to purchase 65 microwave circulators at a cost of $12,772.75 from a California company, Western Microwave, the indictment says.

According to the indictment, Nachtrab sent the equipment to a West German firm, Contacta Project Engineering and Consulting, headed by Klaus Talleur, the fourth defendent.

Talleur then re-exported the equipment to Landau in Austria, the indictment says.

Microwave circulators are a standard component in microwave radar and communications systems. Ken Schoniger, president of Western Microwave, said the circulators in question were "standard textbook units" based on freely available technology developed about 15 years ago.

Export of circulators and the other components are controlled on the grounds that they have military applications that could weaken the security of the United States.