A former Metro repairman was sentenced to three years' probation in federal court here yesterday, and ordered to repay $3,400 that prosecutors said was his profit in a fraudulent Farecard scheme.

Patrick Wright Chandler of Suitland had worked for a subcontractor for Cubic Western Data, which held the Farecard maintenance contract, from December 1978 to March 1979. According to prosectuors, Chandler figured out how to manipulate vending machines to print 340 Farecards, valued at $20 each, for free.

Chandler pleaded guilty to one count of wire fraud last May before U.S. District Court Judge Gerhard Gesell, who imposed the sentence yesterday. The wire fraud charge stemmed from Telephone calls made to arrange sales of the Farecards.

Chandler told Gesell yesterday he printed the cards in case he got a job in downtown Washington and needed to ride the subway every day to work. Chandler said he put the Farecards in a drawer at his home where they remained for two months until he decided to start selling them at half price to help pay off debts.

Chandler's father, Joseph George Chandler Jr., a retired federal employe, of Waldorf, Md., allegedly helped sell the Farecards to his former coworkers at the Office of Personnel Management. The elder Chandler pleaded guilty to one count of receiving stolen property, a misdemeanor, and was sentenced yesterday by Gesell to pay a $350 fine. Joseph Chandler received no income from the sale of the cards, according to government evidence.