John Grist Brainerd, 83, an engineer who headed a team that designed the world's first electronic computer amid wartime secrecy. Former director of the Moore School of Electrical Engineering, Brainerd headed a University of Pennsylvania team that designed and assembled ENIAC, a calculator that filled a 30-by-50-foot room, weighed 30 tons and contained 18,000 electronic tubes. The machine, designed for such tasks as aiming missiles and long-range guns while taking into account variables such as temperature, wind and Earth movement, carried the official name Electronic Numerical Integrator and Computer. It was unveiled on Feb. 1, 1946, at a cost of $486,000 and its 18,000 vacuum tubes were used to calculate in minutes what had previously taken scientists months to figure. Two of Brainerd's associates on the ENIAC project went into business together producing a computer they called UNIVAC. In Kennett Square, Pa., on Monday.