Members of the National Treasury Employees Union will be out in force tomorrow picketing firms owned by the W.R. Grace Co. in Atlanta, Austin, Tex., Boston, Cincinnati, Cleveland, Dallas, Los Angeles, New York, Philadelphia, San Francisco, Seattle and Washington.

The union is demanding an apology from J. Peter Grace, who headed the President's Private Sector Survey on Cost Control. That group, better known as the Grace Commission, recommended major changes in federal pay and benefits. Among other things, the Grace Commission said that federal workers enjoy pension benefits that are much better than those available to most American workers.

Federal and postal unions say that many of the conclusions of the commission were exaggerated, or just plain wrong. NTEU, the National Federation of Federal Employees and other federal-postal unions have been urging members to boycott Grace-owned stores and restaurants until Grace apologizes or modifies his recommendations for cutbacks. The lunch-hour picketing here will be at the Devon Bar and Grill, 2000 Pennsylvania Ave. NW.

In recent weeks members of the National Association of Letter Carriers and the American Postal Workers Union have picketed hotels and clubs, in Erie, Pa., and Buffalo, where Grace was talking about his deficit-cutting proposals.