WASHINGTON, Oct. 14 - A federal panel of medical experts studying illnesses among veterans of the 1991 war in the Persian Gulf has broken with several earlier studies and concluded that many suffer from neurological damage caused by exposure to toxic chemicals, rejecting past findings that the ailments resulted mostly from wartime stress. Citing new scientific research on the effects of exposure to low levels of neurotoxins, the Research Advisory Committee on Gulf War Veterans' Illnesses concludes in its draft report that "a substantial proportion of Gulf War veterans are ill with multisymptom conditions not explained by wartime stress or...