Twelve employes of the Washington Suburban Sanitary Commission--including three who were convicted of theft--have been fired as the result of the water-and-sewer agency paying at least $40,000 for equipment it did not want and did not receive.

Montgomery County District Court Judge Edwin Collier on Monday found a former WSSC garage mechanic, Jerome Dankos, 30, of Hyattsville, guilty of theft and sentenced him to one month in jail. In March, another mechanic, Scott Gorzkowski, 33, received a $500 fine and was ordered to repay $495 to WSSC. Last month, in Prince George's District Court, Gorzkowski was fined $250, ordered to pay $540 in restitution and sent to jail for a weekend.

WSSC investigators said the scheme, brought to light more than a year ago, centered on Melvin H. Minor, a garage and maintenance supervisor. Minor, 43, a former Riverdale mayor, pleaded guilty in Prince George's District Court in July to theft and was given probation before judgment, with no fine or imprisonment.

Alexander H. Zion II, who investigated the case for the WSSC with help from Prince George's County police, said Minor authorized "field purchase orders," for quickly needed supplies for the commission's heavy equipment. Minor and the employes involved then bought the equipment and took it home, Zion said.

In addition to those charged, nine other employes who worked at WSSC garages in Bladensburg and Silver Spring admitted involvement and were fired, according to Zion. He said those employes also voluntarily paid the WSSC about $6,000 in restitution.

Zion said the illegal purchases included a $1,000 snow blower, air compressors, space heaters and an assortment of motor parts and equipment. "The system which WSSC had was good," said Zion. "But trust and responsibility has to be laid upon someone somewhere," and when the manager was involved in the scheme, the system failed, he said.

"There was no mad and rampant theft" problem, Zion said, but the purchase order system has since been been altered to make thefts less likely.