Two Washington women who work for the Department of Health, Education and Welfare pleaded guilty yesterday to charges that they illegally received District of Columbia welfare payments while working for the federal agency.

Suzanne W. Kenney, 25, of 1621 Butler St. SE, pleaded guilty in U.S. District Court to a criminal information alleging that she obtained a $203 welfare grant by failing to disclose "material information" to the city.

Kenney is a psychiatric nursing assistant at the federally operated St. Elizabeths Hospital. She had been receiving legal welfare payments until she started to work at St. Elizabeths in the fall of 1975, according to Assistant U.S. Attorney Michael L. Lehr.

In a separate case, Maxine Ashton, 39, pleaded guilty to a charge of making false pretenses in connection with the receiving of a $248 welfare check. Her lawyer, Michael Walsh, said she once was a legal welfare receipient and told welfare officials that she had returned to work, but that welfare officials continued to send her checks.

Both cases resulted from "Project Match," an HEW program began last year in which the names of HEW workers were compared by computers with the names of D.C. welfare recipients. A study of the computer watch-up found that 142 HEW workers were suspected of illegally receiving welfare payments.