Swiss authorities have arrested a German national who was indicted here along with his wife on charges they fraudulently obtained more than $500,000 in tax refunds from the Internal Revenue Service over the last 8 1/2 years.

According to informed sources, Arno Arndt arrested by Swiss officials on April 6. He is being held without bond while Swiss authorities determine whether him to the United States.

Arndt's wife, Marlise, also was arrested but was later released. She could be prosecuted in Switzerland for her part in the alleged fraud, but under Swiss law, she cannot be extradited.

The Arndts were indicted on charges of filing 137 false tax returns to obtain refunds from the IRS in what authorities said was one of the largest tax fraud cases in U.S. history. Arndt and his wife allegedly prepared phony W-2 wage statements using more than 60 false names to obtain the funds. The indictment was unsealed March 16, 14 months after it was returned by a grand jury. Following an unsuccessful effort by the U.S. to persuade Swiss officials to extradite the couple.

Officials in the Swiss embassy said they had only sketchy details concerning the arrests in Switzerland. Asistant U.S. Attorney Raymond Banoun, who is handling the case here, declined to comment on the progress of the investigation.