The future, says energy specialist Denis Hayes, is not what it used to be. Americans use a million barrels of oil every 90 minutes. We produce two new cars for every new baby and we build three hydrogen bombs every day.

Elbow room is running short: land cannot be a park, a farm and a coal mine simultaneously, and we need all three. Seen in that light, Hayes' "Rays of Hope" at first seems misnamed.

Hayes is the man who brought us Earth Day, the nationwide happening in 1970 that is sometimes credited, or blamed, for getting America stirred up about pollution. In his new book, Hayes tries to prod us into action once again, this time about energy.

Even energy czar James Schlesinger would agree with the theme of the book: "We are NOT running out of energy. However, we are running out of cheap oil and gas." Schlesinger has not so far demonstrated Hayes' faith, however, in a solar-powered alternative energy future.

Hayes gives at least a few of his densely written paragraphs to every alternative energy source ever considered, from fermented water hyacinths to laser-fed nuclear fusion. His prejudices are frank: Fusion gets just twice as much space as the one paragraph describing inventor Steve Baer's house, where one wall consits of metal barrels filled with water that stores heat.

The rays of hope are the sun's, Hayes argues, and he makes no effort to stage a balanced debate with those who prefer nuclear power: "Most nuclear issues are not amenable to proof; they are matters of judgment." If pro-nuke people would disagree with that, they might also deny that "at the heart of the [nuclear power] issue is the threat of holocaust."

Surely, however, that is the bottomline, gut-level point that nuclear opponents are really making as they agonize over leaking pipes and isotope traces, and Hayes may be doing the entire argument a favor by spelling it out.

In his survey of solar-power solutions, Hayes points out that firewood as approaching crisis shortages in much of the Third World; that food production, packaging and distribution are major energy gluttons in this country; and that industrial energy use is roaringly inefficient.

He never really answers the question solar-energy critics always bring up first: How can the sun power a jet plane or fire a steel mill, especially at night? He insists, however, that the sun can power enough other aspects of life to change everything beginning right now, if Americans will only pay attention and stop squandering the energy resources they already have.

"The cheapest and best energy option for the entire world today," Hayes concludes, "is harness the major portion of all commercial energy that is currently being wasted."