LONDON — Describing the latest doping allegations leveled against track and field as a “declaration of war,” Sebastian Coe rushed to the defense of the IAAF’s drug-testing system Tuesday and said it was time to “come out fighting” to protect the reputation of the sport. In an exclusive interview, Coe gave his first extensive comments following reports by German and British media outlets alleging that the IAAF had failed to act on suspicious blood tests involving hundreds of athletes over a 10-year period. “It is a declaration of war on my sport,” said Coe, an IAAF vice president.