Sergeant Jim Chee and his wife, Officer Bernadette Manuelito, again star in one of the Navajo Nation's crime thrillers, THE SACRED BRIDGE. As times modernize, Chee, getting a little older than the confident young go-getter of the early years, is looking at the past and considering becoming a traditional healer. Bernie, still with the fire of youth (and with more work now Anne Hillerman is writing her story) gains experience in her first undercover assignment.   I first read of Jim Chee in the late Tony Hillerman's A Thief Of Time, which focused on ancient artifacts being dug up and sold. The latest episode revisits this in a more nuanced fashion. Lake Powell, which Chee visits on a few days' vacation, is shrinking now, but when created this human-made reservoir drowned many caves and Native sites. If people removed artifacts at the time of flooding, they were working to preserve the culture, so is that still a crime? Since Chee is a detective, of course, he has a detective's vacation in which he comes across a body and is roped into the investigation.   With Chee away, Bernie comes into her own, assuming more responsibility and pursuing brazen, modern, criminals. Ones who don't respect Navajo authorities and don't hesitate to kill. This novel is as slow-paced a story as usual for much of the book, because of the long distances involved and many conversations needed. But when the pace picks up, it races.