Bernard O. Williams, 42, formerly of Weatherly but residing in Philadelphia, was fatally stricken with a heart attack while driving on the Pennsylvania Turnpike, yesterday. Five other family members were in his car. Williams' son, Bernard, 16, was riding in the front seat and noticed his father slump over the steering wheel. Bernard grabbed the wheel and pulled the vehicle off the highway, then used mouth-to-mouth resuscitation in an attempt to revive him.