In the hope of reviving interest in the Olympic Games after last year's ratings plunge for the Summer Games, the NBC television network and its two cable siblings, CNBC and MSNBC, plan to televise 373 1/2 hours between them of the Salt Lake City Winter Games next year, Bloomberg News reported Wednesday. The wire service said that NBC has provided potential advertisers a 27-page report in which its program schedules were disclosed. The network is also promising ad buyers an average 17.8 rating during primetime. In 1998 CBS averaged only a 16.3 rating after guaranteeing advertisers a 19.6. NBC presumably figures that an all-live Olympics on U.S. soil will heighten interest in the event, scheduled for Feb. 8-24.