A former accounting technician at the Federal Election Commission pleaded guilty in U.S. District Court yesterday to embezzling more than $550,000 in government funds by submitting 22 fake vouchers to the Treasury Department during a three-month period last summer.

Michael J. Rupenthal, who was fired from his $20,775-a-year FEC job shortly after his arrest on Sept. 7, faces a possible 10 years in jail and a $10,000 fine for his guilty plea to a charge of embezzlement of public money.

Assistant U.S. Attorney Charles H. Roistacher told Judge Harold H. Greene yesterday that if the case had gone to trial, the government could prove that Rupenthal, 35, mailed the checks to his farm, called "Stonebrook," in Lovettsville, Va. and deposited the money. After his arrest, Rupenthal admitted to the scheme, Roistacher said.

Investigators said yesterday that the theft was discovered when FEC and Treasury officials, who had noticed discrepencies in the agency's accounts during the summer, started examining records while Rupenthal was on a week's vacation. The investigators said it was then determined that Rupenthal's name was on a list of issued checks.

As a result, the FEC was able to stop payment on about $160,000 in checks which Rupenthal had issued either to himself, another person or various businesses, law enforcement officers said yesterday.

Since then, investigators from the FBI and the U.S. Secret Service said that they have accounted for all but about $70,000 of the $403,559 in checks that were cashed by Rupenthal. Of that total amount, agents said they have seized $189,000 in assets, including a $20,000 Steinway grand piano, three vehicles including a 1982 Cadillac and a 1983 BMW, $30,000 worth of designer clothes purchased from a Ralph Lauren Polo Shop; crystal, furniture, silver and $9,000 worth of jewelry.

In addition, agents have frozen another $143,000 in assets, including Rupenthal's 58-acre farm in Louisa County, Va., which includes a historic farmhouse; a deposit on furniture and stocks, investigators said.

All the purchases were made between last June and September, investigators said. Another $2,900 was left in a bank account, the investigators reported.

Green scheduled sentencing of Rupenthal, who is free on a $20,000 surety bond, for Nov. 15.