A 35-year-old New Stanton, Pa., man who was carrying about $170,000 in cash and gold coins was arrested Thursday night in Union Station after an employe of a rental car firm discovered ammunition in a car that the man had returned, U.S. Park Police reported yesterday.

Dennis J. Markle, who listed his occupation as a self-employed dealer in gold and silver, was arrested by a park police officer who had been called by the Avis rental car firm, a park police spokesman said.

According to court documents, Ozzie Osbonne, an Avis employe, found a magazine clip loaded with ammunition in an Oldsmobile that had been rented by Markle. When park police officer R. Munsky arrived at the station, an Avis employe pointed out Markle sitting in the station.

Markle was taken to park police headquarters, where he telephoned a lawyer and then agreed to allow a search of his baggage, according to the court papers. Police said they found $45,000 in cash and 195 Canadian gold coins valued at $125,000, and a jar containing marijuana and some narcotic pills. No weapons was recovered.

Markle was charged with possession of marijuana and dangerous drugs and possession of unregistered ammunition. He was arraigned in D.C. Superior Court and released on personal bond.