De Lorean, gorillas, Grant and Lee, and more; Gorillas in the Mist, by Dian Fossey. Boston: Houghton Mifflin Company. 326pp. $ 19.95.

If you're ever charged by a 350-pound gorilla, hold your ground. The chest-beating primate is just bluffing, if world authority Dian Fossey knows anything about it.

Fossey faced down more than one excited animal in the gorillas' rain forest home bordering Rwanda, Uganda, and Zaire. Spending her days crawling through the bush observing gorilla life, and nights recording data, ''It never dawned on (her) that exhausting climbs along ribbons of muddy trails . . . would not be everyone's idea of heaven.''

She shares sensitive photographs and vignettes of the family-oriented, disturbingly humanlike creatures. There is faithful Digit (''He stood passively gazing down at me before patting my head''), and little Coco, trapped and destined for a zoo (''Suddenly she began to sob and shed actual tears'').

Tragically, this gorilla species, recognized only in the last 80 years, may be extinct before the year 2000. Already nearby villagers turn forest into farmland, and poachers ensnare gorillas in traps.

You've probably never thought about mountain gorillas before, but - fair warning - after reading this book you will. It's as though Dian Fossey, in her own concern, has handed each reader the responsibility of caring about the fate of these gentle primates.