President Bush on Wednesday tapped a dozen young professionals to spend the next year on special high-level government assignments as White House Fellows. The fellows, chosen from nearly 1,000 applicants, will begin their 12 months of government service on Sept. 1. A presidential commission helped make the final selections from 33 national finalists. They are the 26th class of fellows chosen since the high-level internship program was launched in 1964. They will work as special assistants to Bush's own staff, the vice president and members of the Cabinet. The new fellows are: _Andrew I. Batavia, 32, of Washington, a disability expert who directs the Health Services Research Program at the National Rehabilitation Hospital Research Center. _Samuel Dale Brownback, 33, of Topeka, Kan., the Kansas secretary of agriculture. _Robert Bruce Chess, 33, of Palo Alto, Calif., president and co-founder of Penederm, a biotechnology company. _Jody Ann Greenstone, 32, of Greenville, S.C., vice president in public finance of the Robinson-Humphrey Co., a subsidiary of Shearson Lehman Hutton. _Robert R. Grusky, 32, of Croton-on-Hudson, N.Y., a vice president in the investment banking division of Goldman, Sachs & Co. _Air Force Capt. Willie Arthur Gunn, 31, of Fort Lauderdale, Fla., a circuit defense counsel defending service members in complex criminal cases in five Western states. _Air Force Maj. Randall Herman Kehl, 36, of Albuquerque, N.M., an attorney with the Judge Advocate General's office in Washington. _Navy Lt. Cmdr. John William Miller, 32, of Annapolis, Md., the head of the leadership section in the Naval Academy's Department of Leadership and Law. _Eric McLaren Phillips, 37, of Maplewood, N.J., a Guyanese-born district manager for AT&T International Communications Services. _Air Force Maj. Edward Augustus Rice Jr., 33, of Yellow Springs, Ohio, a manager in the Air Force's directorate of plans and operations in Washington. _Joseph E. Samora Jr., 34, of Albuquerque, who is chairman of the New Mexico Public Service Commission. _Kimberly Till, 34, of Prattville, Ala., an international management consultant with Bain & Co. in London. Appications for the 1991-92 program are available from the President's Commission on White House Fellowships, 712 Jackson Place, N.W., Washington, D.C. 20503.