AT 4:17 PM TODAY the earth, speeding along at the present clip of 66,000 miles per hour, will have circled the sun exactly ten times since two men inside a spidery little space craft wrapped in gold tin foil hit the dust of the Sea of Tranquility.

July 20, 1969 doesn't seem like such a long time ago. Most of the problems and personalities of that day have changed, but to those who grew up in the sixties, they were facts of life. The body count from Viet Nam, every night from Huntley and Brinkley, interrupted by cigarette commercials. Ghetto riots in the summer didn't make the news unless they were big ghetto riots (the little ones were expected.) July was too hot for big anti-war protests, though; demonstration season was late spring and early fall. Joe Namath's Jets has embarassed the NFL, while the Mets, on the way to the World Series, split a double-header with Montreal. In the Middle East, the war of attrition entered a new phase, as the Israelis began using their air power on Egyptian bases.

Finding the diversion welcome, most of the world was watching as Neil Armstrong slowly descended the steps of the lunar module (LEM--remember?), hesitated for a moment on the final rung, then placed the first human bootprint on another world. ("The surface appears to be very, very fine-grained," Armstrong observed while his friend "Buzz" waited to join him, "it's almost sort of a powder.") It was bona fide Big Stuff. CBS and provided 31 hours of continued coverage; ABC naturally stopped after 30. "Save us a copy," the astronauts radioed back, when informed that the New York Times had used the largest headline--"MEN WALK ON MOON"--in its history. Nine more moon landings were planned to follow Apollo XI, and NASA officials glibly predicted that a permanent space station in earth orbit as well as a lunar base would be established by the mid-seventies.

But the novelty of going to the moon, and of space exploration in general, wore off quickly, in part because the government's commitment to those programs came out of political and military expediency ("Beat the Commies"), rather than any scientific motivation. In aligning itself in the public eye with Johnson and Nixon, the Pentagon, and other symbols of conservatism, NASA unintentionally hurried its own decline. For these "friends" of the space program aided it only when such help was good policy.

THE DAY APOLLO XI reached the moon Nixon and Co. ended their first six months in office by celebrating not the landing of the Eagle but the drowning of Mary Jo Kopechne in Edward Kennedy's car at Chappaquidick the morning before. By the time "Tranquility Base here, the Eagle has landed" reached Houston, the White House had already dispatched Tony Ulasewicz to dig up all the dirt on the incident. When space lost its public appeal and propaganda value, most "supporters" dropped it.

Opposition had been growing long before Apollo XI left the pad at Cape Kennedy. The $25 billion price tag for the manned space program, spread out over ten years, provided a nice target for those who thought we should "solve our problems on earth before we worry about space." The public image of NASA and space exploration evolved into one of tremendous waste, of massive expenditures for little or no return.

So when moonshots started boring people and networks no longer felt like covering them in depth, support for space fell faster than Skylab. Nixon, whose obnoxiousness had interrupted the moonwalk, turned around and canned the last three Apollos. The funds for the proposed space station were cut sharply, meaning that Skylab would be built on the cheap, out of a mishmash of spare parts from the Apollo programs. NASA wanted to put the station into a higher orbit than the one ended in Australia last week, but the money wasn't there.

With the decline of the manned program came an equal lack of enthusiasm for automated missions to explore the planets. In 1972, with help from the White House, Congress eliminated the "Grand Tour" project, which would have taken advantage of a rare (once every 180 years) planetary alignment to survey the entire outer solar system. Those missions that were approved often did not receive funding for complete analysis of the return data. Others--to map the moon and check it for metal deposits, to research solar phenomena, to rendezvous with Halley's Comet--never got past appropriations subcommittees.

Nevertheless, the solar system we knew ten years ago pales in comparison to the picture we have of it now. Back then, there were very few definable worlds: the Earth, the moon, fuzzy pictures of Jupiter and Saturn, and a few cryptic shots of Mars.

NOW IT'S DIFFERENT. Mariner 10 went to Mercury and found a heavily cratered, dessicated world; and to Venus, sending thousands of views of the carbon dioxide clouds that shroud the planet. Mars, thought by some to be as "boring" as the moon, turns out to be a world with as many oddities and mysteries--with the probable exception of life--as earth. (Where else can you jump off a four-mile cliff or find a volcano that would stretch from Harvard Yard to Toronto?) The planet, as Viking I showed us, looks like a nice place to go for a walk. Its two tiny moons have also been seen up close now, and one of them, Phobos, is covered with parallel grooves as if it had been assaulted by some interplanetary version of the Hell's Angels.

Farther out, beyond the asteriod belt, Jupiter has been visited by several unmanned spacecraft, most recently Voyagers I and II. The most massive planet in the solar system has no surface to speak of, but the patterns in its stormy atmosphere and bands of swirling colors would please Dali. Also, Saturn no longer has a monopoly on rings. For hundreds of years, it looked that way, but since 1977 rings have been discovered around both Uranus and Jupiter. Surprise.

As Voyager I flew past Jupiter this March, satellites that has been mere specks of light suddenly became full-fledged whirls, each with its own pecularities. Io, a conglomeration of soft red and white blotches, reminded one scientist of a cheese pizza. Eight volcanoes were photographed in mid-eruption. A frosty covering of ice dominated another of the satellites; still another is criss-crossed by ridges that resemble those caused by continental drift on earth. Eleven worlds have come into focus since Apollo XI.

The manned program, in virtual hibernation since the last Skylab mission in 1973, will reawaken when the shuttle begins operation next year. Plans call for several missions each year, with the half spaceship/half-glider confined to earth orbit.

THE MOON STILL WAITS. There are no plans to go back. Some day, though, assuming we don't destroy ourselves first, humans will probably quicken the pace of what one writer has called "our hesitation waltz into space," and return to the lunar surface.

If, perhaps, they would like to find the deserted Eagle, and maybe take a few pictures or inscribe some graffiti on the "we-came-in-peace-for-all-mankind" plaque, it's not too tough. Just head east from Keppler, continue past Copernicus, and hang a right at the Sea of Vapors. If you hit the Sea of Fertility, turn around; you've gone too far.

When they get there, they might want to switch on the experiments left behind by the Apollo astronauts. Sending data back to earth about moonquakes, solar wind levels, and so on, they were still operating in September 1977 when it was decided that we couldn't afford to pick up the signals. So the instruments were turned off. Only a few scientists were upset; no one else cared one way or the other. Welcome to the Space Age.