The President's Private Sector Survey on Cost Control yesterday proposed establishing a "Combined Welfare Administration" that would run the aid to families with dependent children (AFDC), food stamp and Medicaid programs with an eye to avoiding duplication.

In six more reports released yesterday, the survey recommended ways that it said the government could save $30.1 billion over the next three years. In 22 reports so far, the task force has recommended $160.81 billion in savings and potential new revenue over that time.

J. Peter Grace, who chaired the survey, said the latest reports show $10.211 billion in savings and revenue opportunities could be realized in user charges; $9.398 billion in banking and investment related boards and commissions, and $5.856 billion in low-income standards and benefits.

He said $3.3 billion could be gleaned from business-related boards and commissions; $719 million from land, facilities and personal property management, and $635 million from the State Department, Agency for International Development and U.S. Information Agency.

Grace said he met with President Reagan and Cabinet members Sunday and, "The comments were very favorable all around. They have a computer system set up that will completely embrace the 4,000 suggestions we will make overall, and set deadlines for achieving them. We have contact with the White House at an instant's notice."

About 65 percent of his group's recommendations will require the approval of Congress, Grace said.