In retrospect, it was merely a matter of time before Tom Hayden would finally proclaim himself an Indian. For a quarter century or more, Indians have been Hayden’s favorite people — equaled in his affections for only a few years by the Communist Vietnamese. But whereas Communist imperfections belatedly caught Hayden’s eye, long after the last blood of American troops had stained Indochinese soil, the romance of Indians still retains its hold on the California state senator, delegate to last week’s Democratic convention, and onetime leader of the New Left.

Best of all, Hayden is now one of them. His transformation is recounted in his new book, The Lost Gospel of the Earth (Sierra Club Books, 267 pages, $ 22), a work of environmental theology that will solidify Hayden’s reputation as his generation’s most nimble spokesman for whatever leftist enthusiasm dominates the day.