BOOK REVIEW / SCIENCE : Reawakening Our Appetites for Exploring the Heavens : PALE BLUE DOT: A Vision of the Human Future in Space <i> by Carl Sagan</i> ; Random House $35, 427 pages

In the ‘30s and ‘40s we wanted to reach space to bless (or bombard) the Martians. In the ‘50s and ‘60s, we wanted to get there before the Russians.

But what lures us toward the heavens now? Not the promise of finding life, for even our supreme stargazer, Carl Sagan, admits here that our probes have failed to encounter “a cricket or a blade of grass, or even, so far as we can tell for sure, a microbe.”

And surely not the triumphs of NASA, for as Sagan also acknowledges, “In the ‘80s and early ‘90s, many people saw the U.S. space program as . . . a succession of catastrophes--seven brave Americans killed on a mission whose main function was to put up a communications satellite that could have been launched at less cost without risking anybody.”

“Pale Blue Dot” is consequently a wan blue book compared to Sagan’s ebullient celestial celebration, 1985’s “Cosmos.” Railing against “our convenient and satisfying myths,” Sagan is sometimes bitter:

“How is it that hardly any major religion has looked at science and concluded, ‘This is better than we thought! The universe is much bigger than our prophets said--grander, more subtle, more elegant. God must be even greater than we dreamed?’ Instead, they say, ‘No, no, no! My god is a little god, and I want him to stay that way.’ ”

Sagan’s most disingenuous moments come when he tries to appeal to the little god within us by promising it fun and riches. For instance, he gushes that the Neptunian satellite Triton “may offer a skiing experience unrivaled in all the solar system,” and he predicts that spacecraft rocketing back from excavations on Mars may be “stuffed with gorgeous multi-carat diamonds.”

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Fortunately, Sagan inspires more often than he condescends in these pages. Just as one of our Voyager probes was about to high-tail it out of the solar system at 40,000 miles per hour, for instance, he persuaded NASA to pivot its camera back to Earth. What the probe discerned from 3.7 billion miles away--a pale blue dot--is unimpressive on its face.

But, Sagan writes:

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know . . . every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant . . . every saint and sinner in the history of our species lived there--on a mote of dust suspended in a sunbeam.”

Even those who are more amused than amazed by Sagan’s famous incantation, “billions and billions of stars,” cannot fail to be moved by the stunning photos reproduced here. One, taken by the Hubble Space Telescope after its visit to the ophthalmologist, shows only one-hundred millionth of the sky, yet contains over 100 trillion stars.

Make you feel small? Well, this, of course, is Sagan’s aim. He wants nothing more than to debunk the notion of 17th-Century poet John Donne that “man . . . is all. He is not a piece of the world, but the world itself; and next to the glory of God, the reason why there is a world.”

That quote comes from the 17th Century, and Sagan believes that the thinking behind it helped turn ambitious “hunters . . . wanderers . . . (and) explorers . . . bounded only by the Earth, the ocean and the sky” into “unadventurous, overweight, careless” moderns.

Clearly, this is a case of over-romanticizing the former at the expense of the latter.

But there’s no disputing Sagan’s point that kids--who seem to be born asking questions like “What’s the birthday of the world?”--somehow have “the science beaten out of them by society.” And you have to admire his attempt to help reawaken our lust for exploration and understanding.

Toward this end, Sagan makes genuine progress in these pages, most notably in illustrating how a single spacecraft--costing no more than one strategic bomber--could make its way through the thick reddish clouds of the Saturnian moon Titan.

Descending through Titan’s atmosphere, which still retains some of the hydrogen-rich gases that existed when organic materials were being massively generated on our own planet, it could do more than blanket a city with cluster bombs. It could help explain the very genesis of life on Earth.