An accounting examiner at the Federal Election Commission was arrested yesterday and charged with diverting nearly $400,000 in government funds to his personal use by preparing vouchers for nonexistent commission expenses.

Michael James Rupenthal, 36, was arrested by FBI and Secret Service agents yesterday when he reported for work at the commission's office, 1325 K St. NW.

Rupenthal, who was placed on administrative leave with pay from his $20,775-a-year FEC job, allegedly told investigators after his arrest that he used the money to purchase a 1982 Cadillac, a 1983 Datsun, a 1982 Datsun pickup truck, a farm in Louisa County, Va., jewelry, household crystal, stocks and several other items, Assistant U.S. Attorney Richard L. Beizer said at a bond hearing yesterday.

Investigators said they found that Rupenthal issued at least 16 phony vouchers since June 22 that caused government checks to be sent to his Lovettsville, Va. home in northern Loudoun County, according to an arrest affidavit filed in U.S. District Court in Washington. The checks, which were made out in the names of Rupenthal, a business and another person, ranged in amount from $798.49 to $74,598.62, the affidavit alleged.

U.S. Magistrate Arthur L. Burnett ordered Rupenthal held on a $20,000 bond.

Richard S. Stern, Rupenthal's attorney, told the magistrate that his client has cooperated with investigators and has no previous criminal record.

Beizer said that Rupenthal has agreed to turn over the items he allegedly purchased with the government money. An FBI spokesman said the vehicles and several other items were seized yesterday.

Rupenthal has been charged with one count of mail fraud in connection with a $48,526 government check issued Aug. 3.