Another potential block-buster set of hearings before the Post Office-Civil Service Committee has been set by Chairman James M. Hanley (D-N.Y.). say the government may be one of the most careless, indifferent employers when it comes to workplace safety and health.

He has set April 3, 4 and 10 as hearing dates on what he calls the "skyrocketing" $5 billion costs Uncle Sam is running up because of worker injuries and health problems.

Hanley, and money others in town, have been in touch with workers at the gaint Hill Air Force Base in Utah. They complain that employes there have an "abnormally high" rate of cancer and other diseases that they blame on exposure to hazardous chemicals in Air Force cleaning and repair shops.

The comittee plans to make Hill AFB the focus of its early hearings, with data compiled over a period of years by the head of the American Federation of Government Employees union at the base. AFGE leaders, using Air Force medical records and reports from employes, have contacted various occupational health experts and covinced them -- and most of the Utah congressional delegation -- that a major health problem exists at Hill. (Air Force officials say necessary steps have been taken to protect workers, and provide them with safe work environments when dealing with toxic chemicals).