Local social service agencies are bracing to absorb a projected $20 million deficit in the Maryland Department of Human Services budget, a shortfall that could have a significant impact on services at a time when welfare rolls are swelling.

Local directors said they have been told to prepare to scale back programs, freeze hiring and, perhaps, eliminate some programs that are not mandated by the state or federal governments. Programs such as Aid to Families with Dependent Children, child protection, adult protection and foster care would not be directly affected by budget cuts, but local programs and the number of social workers available to help clients could be reduced.

"If that figure holds, it would have a significant impact," said Henry L. Gunn, director of the Prince George's County Department of Social Services. The state can't absorb "a $20 million deficit without cutting services at the local and central offices," he said.

"A significant impact at this level is unavoidable with the projected deficit," said Robert S. Caulk, director of the Montgomery County Department of Social Services. "Any planning would have to look at how we . . . minimize the impact on clients."

State officials would not confirm the amount of the projected deficit, saying that the final figure won't be known until August.

The expected deficit in the Human Resources Department's $859 million budget comes at a time when the number of people receiving welfare in Maryland has climbed dramatically for the first time in a decade. In 1989, the number of families receiving AFDC, the state's main welfare program, grew by 7 percent to more than 67,000, reversing a 1980s pattern of declining or steady welfare rolls.

In Prince George's County, where an increasing drug trade has hurt families, the AFDC caseload climbed by 20 percent over the previous year.

At the same time, the state economy has faltered and the amount of surplus money has been greatly reduced. Last year, the General Assembly gave the Human Resources Department a $44 million supplemental grant to cover shortfalls in its budget.

But this year, Department of Human Resources Secretary Carolyn W. Colvin said, "I can't assume that human services will receive the top priority. Many of {the state} agenices will be needing the same dollars. We always plan for the worst."

Local directors were reluctant to say what programs would be eliminated or reduced. Examples of discretionary programs include an intervention project in Prince George's that aims to keep troubled families together and a Montgomery program that provides county jobs to the unemployed instead of welfare.

A hiring freeze "is one of the last things we would want to consider," Gunn said. "Any freeze in {workers} would have a negative impact on service delivery."

In Baltimore, Director of Social Services Shirley E. Marcus detailed in a memo plans to shift some positions and eliminate several programs, incuding the sexual abuse treatment program and the Vivian E. Washington Group Home for unwed teenage mothers.