July 1969: The moon rocket, towering 37 stories tall on its pad, began its skyward climb with 10 million pounds of thrust. Less than half a second later, a pump in one of its 43 engines drew in a stray metal shaving and blew up. The entire booster fell back to Earth and exploded with the force of a small nuclear bomb, wiping out the launch complex on the remote steppes of Central Asia. The catastrophe, unknown to most of the world but monitored by U.S. intelligence, effectively ended the "space race" for the Soviet Union.

Thirteen days after the failure of the Soviet N-1 rocket, half a world away, other men in other control rooms watched in an agony of suspense as their own fire-breathing monster rumbled and roared to life on a Florida launch pad. This time, the rocket didn't falter. Three Americans were on their way to a historic lunar landing and -- even though much of the competitive steam had puffed out of the race -- a stunning victory for their side.

The public focus since then has been mostly on the technology, the science and the sheer human audacity of it all, but the driving force behind the project was geopolitical.

More than a decade earlier, on Oct. 4, 1957, Russian engineers had fired the first round in the battle for the new "high ground" with the launch of a seemingly inconsequential 184-pound sphere: a radio transmitter hooked up to a thermometer, powered by a pack of chemical batteries. Once in orbit, Earth's first artificial satellite, or Sputnik ("companion"), emitted a benign signal: "Beep, beep, beep . . ."

Yet to then-Sen. Lyndon B. Johnson, entertaining guests at his ranch in the Texas hill country when he got the news, "in some new way, the sky seemed almost alien," he wrote later. Americans who had thought themselves technologically superior and safely isolated by two great oceans now suddenly felt vulnerable.

How could a primitive little space ball discombobulate a powerful nation? Science fiction enthusiasts had long dreamed of space travel for peaceful purposes, but the real Space Age dawned with more sinister meaning. Because Sputnik had been launched on an intercontinental ballistic missile, Soviet leaders hailed the feat as proof of their ability to deliver hydrogen bombs at will -- and of the superiority of communism over democracy. Prowess in space emerged as a Cold War propaganda tool, with astronauts as surrogate combatants.

Even so, it wasn't until 1961, as the Soviets continued to taunt America with a string of "firsts" in space, that incoming President John F. Kennedy asked his vice president to find out quickly whether there was some way "we could win." As recommended by NASA and the Defense Department, Johnson proposed a lunar landing "to symbolize the technological power and organizing capacity of a nation. . . part of the battle along the fluid front of the Cold War." On May 25, 1961, when Kennedy issued his call to do it before the decade was out, the entire American experience in human space flight totaled just 15 minutes and 28 seconds, the duration of Alan B. Shepard Jr.'s suborbital flight three weeks earlier.

Kennedy himself had second thoughts, in 1963 proposing to the United Nations a joint U.S.-U.S.S.R. lunar project. But Johnson, succeeding the slain president, was determined to make the United States a leader in space.

"The hope that rode on Apollo was the hope for human adequacy in the face of awful challenges," wrote Walter A. McDougall in his Pulitzer Prize-winning history, " . . . The Heavens and the Earth."

But the sense of urgency drained from the space effort as the Soviets failed to keep up the pace of their own triumphs, and liberal advocates for the poor, the environment and other causes attacked the costs of the Apollo program (through 1972), which would amount to $120 billionX in today's inflation-adjusted dollars.

But the push of people and machines toward the moon, for the moment, had an independent momentum. The program had mushroomed into one of the most complex undertakings in human history, engaging a workforce of almost 500,000 people around the country. The fledgling American space program gradually built an understanding of new technologies and human reactions that space flight entails, through the six one-man flights of the Mercury program, which grew from suborbital to orbital missions up to 34 hours and 20 minutes duration, and the ten two-man flights of the Gemini series, which featured the first spacewalk, the first rendezvous and docking of two spacecraft, the first emergency landing, once reaching a (then) record altitude of 739 miles and extending mission duration up to almost 14 days.

But the space program also grew huge and impersonal and, under the pressure of the Kennedy deadline, cut corners. Its most painful lessons emerged from the fire that blazed up inside a prototype command module at the Florida launch complex in January, 1967, killing the crew of Apollo 1. The tragedy led to reforms in management practices and spacecraft design that, according to astronauts and others, were essential to Apollo's later successes. These included four manned flights between October 1968 and May 1969 that paved the way for the lunar landing.

For the men on point, the adventure of Apollo 11 was by turns tedious, exhilarating, exhausting, noisy, eerily quiet, cold, sweaty, smelly, heart-pounding and at times almost beyond comprehension. History had selected them to live out a fantasy that had dominated science fiction for centuries. And perhaps to die.

"I think we will escape with our skins, or at least I will escape with mine, but I wouldn't give better than even odds on a successful landing and return," Apollo 11 crewman Michael Collins would write of his pre-launch mindset. "There are just too many things that can go wrong." Sitting wedged into the right seat of the command module atop the Saturn V moon rocket, flipping switches, in the final hour or so of the countdown, he mused, "Here I am, a white male, age thirty-eight, height 5 feet 11 inches, weight 165 pounds, salary $17,000 per annum, resident of a Texas suburb, with black spot on my roses, state of mind unsettled, about to be shot off to the Moon. Yes, to the Moon."

On launch day, an estimated one million people assembled at along Florida beaches and causeways to witness the departure of the 363-foot-tall Saturn 5, the master work of the German rocket builder Wernher Von Braun and his team at NASA's Marshall Space Flight Center in Huntsville, Ala.

After the four-day transit, Collins remained alone in splendid isolation in lunar orbit while Neil Armstrong and Buzz Aldrin made the historic descent in the insectile lunar lander. Suddenly computer alarms began to sound. The mission might have been aborted then, flight officials say, if not for the foresightedness of Gene Kranz's ground team at mission control -- and the astronauts' steel nerves. A similar situation had prompted Kranz to abort the landing during a simulation, or dress rehearsal, a few weeks back. As a result, Kranz and a group of computer experts had spent long hours familiarizing themselves with each type of alarm, what it meant and how to respond rapidly. Now the decision to proceed, or not, rested with the team's expert on the lander computer, Steve Bales, age 26. As Aldrin and Armstrong, hutling toward the lunar badlands 240,000 miles away, pressed urgently for information, Bales took just seconds before he decided the system was suffering a task overload but would continue functioning, and blurted, "We're--we're `go' on that, Flight." He was later decorated, along with the crew, at a White House ceremony.

When the distracting alarms finally quit and Armstrong focused on the intended landing site looming out his window, he suddenly realized the computer navigation was steering them into a field of potentially lethal boulders along a crater. He took control and began to fly the lander like a helicopter, searching for a clear spot. [See illustration, A6.]

The anxious ground team in Houston was now out of the decision loop. They knew the landing had departed from the plan and was in the hands of the pilots. Reading the telemetry, the ground team saw that instead of hovering slowly, the craft was speeding horizontally over the surface. They didn't know why, or what was taking so long. Hearing only Aldrin calling out the numbers, they instinctively kept quiet except to alert the pair that the lander was running low on descent fuel. When the Eagle finally settled into the Sea of Tranquility, it had less than a minute's worth of landing fuel remaining.

The first lunar tourists spent only about two and a half hours actually walking around outdoors. There, they spent a cold, damp and virtually sleepless rest period curled up in their spacesuits, kept awake by adrenalin, spacecraft noises and the light of the long lunar day leaking in.

Orbiting above, Collins had mastered a nightmarish checklist that included 18 versions of emergency rendezvous with the ascent module after it left the surface. "My secret terror for the last six months has been leaving them on the moon and returning to Earth alone," he thought. However, less than 22 hours after landing, the Eagle's ascent stage shot itself back into orbit for a successful reunion with the craft that would carry the travelers home to global acclaim.

An undertaking that had been born out of the divisions of Cold War had, for a fleeting moment of history, united much of the world in celebration of the human spirit. Even the official Soviet newspaper reported the event on page one -- though not at the top.

A BIG BOOST

Multi-staged rockets increase a spacecraft's launch speed. In Saturn V, three successively smaller rockets, called stages, are positioned on top of one another. As each stage burns and exhausts its fuel, it falls away and reduces the weight of the remaining craft. Then the next stage fires and the rocket continues to accelerate.

* First stage

Engines: Five F-1s

Thrust: 7.6 million pounds

Fueled weight: 5.02 million pounds

Burn time: 2 minutes, 41 seconds

* Second stage

Engines: Five J-2s (The J-2 was the largest hydrogen-fueled engine ever built)

Thrust: 1.2 million pounds

Fueled weight: 1.07 million pounds

Burn time: 6 min. 27 sec.

* Third stage

Engines: One J-2

Thrust: 200,000 pounds

Fueled weight: 262,000 pounds

Burn time: Two burns. The first: 2 min. 27 sec. The second: 5 min. 45 sec.

SATURN V's FUEL

For liftoff, a rocket's thrust must be greater than its weight. A rocket's weight is mostly made up of fuel, so it takes a great deal to launch even a small payload. The ratio of propellant to payload in Saturn V is 50 to 1.

SATURN V

The largest operational launch vehicle ever produced.

Total height: 281 feet, 363 feet with Apollo modules attached.

Total weight: More than 6.3 million pounds, not including Apollo modules.

Cost: About $650 per pound

APOLLO 11

Command, Service and Lunar modules inside casing.

THE RACE TO SPACE

The U.S. manned space program was conducted in three progressively more complex phases:

* Mercury

Objective: Answer basic questions about man's ability to function in space.

Manned missions: Six

System requirement: Sustain the 4,265-pound spacecraft and a single astronaut for 34 hours.

* Gemini

Objective:

Increase knowledge of celestial mechanics and space navigation; test maneuvering skills.

Manned missions: 10

System requirement: Sustain the 7,000-pound craft and two astronauts for 14 days.

* Apollo

Objective: Perform a manned lunar landing and return.

Manned missions: 12

System requirement: Sustain the 100,000-pound craft carrying three men for eight days.

1926: Goddard

1945: German V-2

1957-59: Vanguard

1961: Redstone

1962-63: Atlas

1965-66: Titan

1968-72: Saturn*

1981: Space shuttle and booster

*Apollo 1 and 7 were atop Saturn IB rockets (not shown)

THE RIGHT STUFF

The crew was selected from a field of 29 Apollo astronauts. Each received more than 1,000 hours of formal training for the mission, in addition to years of experience with other space flights. Collins and Aldrin had been astronauts since 1963; Armstrong, a former Navy aviator, since 1962.

* Neil A. Armstrong, 38

Civilian

Commander

Previous flights: Command pilot, Gemini 8 (1966)

Born: Aug. 5, 1930, Wapakoneta, Ohio

* Michael Collins, 38

Lt. Col., USAF

Command Module pilot

Previous flights: Pilot, Gemini 10 (1966)

Born: Oct. 31, 1930, Rome, Italy

* Edwin Eugene "Buzz" Aldrin Jr., 39

Col., USAF Lunar Module pilot

Manned Missions

Previous flights: Pilot, Gemini 12 (1966)

Born: Jan. 20, 1930, Montclair, N.J.

1. LIFTOFF

July 16, 9:32 a.m. (EDT)

The first stage of the Saturn V rocket roars to life, pushing Apollo 11 skyward, reaching a rate of 7,700 feet per second. Apollo 11 reaches an altitude of 38 miles before the first stage separates and falls back to Earth.

2. Second stage firing

9:35 a.m.

Saturn V's second stage fires and pushes Apollo 11 to an altitude of more than 100 miles and a speed of 14,000 mph.

3. Third stage and parking orbit

9:41 a.m.

As Saturn V's second stage burns out and falls away, the third stage begins the first of two burns. Apollo 11 reaches a velocity of 17,500 mph to enter Earth orbit at an altitude of about 120 miles. Apollo 11 circles the globe 1.5 times as the astronauts check their systems.

4. Translunar Injection

12:16 p.m.

With all systems Go, the third-stage begins its second and final burn. Apollo 11 breaks free from Earth orbit on course for the moon, traveling 7 miles per second.

5. Columbia, Eagle docking

12:49 p.m.

About half an hour after the final third-stage burn, the Command and Service Module, Columbia, and the Lunar Module, Eagle, are ejected.

6. Translunar coast

As the Apollo crew coasts toward the moon, they make mid-course corrections by firing Columbia's service propulsion engine. During the coast, Columbia and Eagle are slowly rotated so that the sun's rays evenly warm the craft.

7. Crossover point

As Apollo 11 moves toward the moon, the pull of Earth's gravity slows it down. When it reaches a point of 215,000 miles from Earth (nine-tenths of the way to the moon), the moon's gravitational pull on Apollo 11 becomes equal to that of Earth's. Passing this point, Apollo 11 speeds up, falling into the moon's gravitational influence.

8. Lunar orbit insertion

July 19, 1:28 p.m.

After more than 73 hours of coasting, Apollo 11 prepares for what is essentially a braking maneuver to insert the craft into lunar orbit. It involves the longest firing of the Service Module's engine (nearly six minutes) and must take place on the far side of the moon, out of radio contact with Houston. Apollo 11 slows from 5,600 mph to 3,600 mph. While orbiting, Neil Armstrong and Edwin Aldrin prepare the Eagle for flight.

9. Columbia, Eagle separation

July 20, 1:46 pm

In the Eagle, Armstrong and Aldrin separate from Columbia approximately 68 miles above the lunar surface and fire their engine to begin their descent. Michael Collins remains in orbit with Columbia.

SERVICE MODULE:

Storage unit carrying most of the consumables needed for the mission -- including oxygen, water, helium and fuel -- and the main propulsion engine.

Length: 25 feet

Weight (with crew): 54,074 pounds

Propulsion engine nozzle

Radiation panel

Orbits 14 times

COMMAND MODULE:

Control center housing the three astronauts and reentry equipment. It is the only part of Apollo 11 designed to be returned to Earth.

Length: 10 ft. 7 inches

Weight (with crew): 13,090 pounds

DID YOU KNOW . . .

* Computer Constraints

Apollo 11's on-board computer was extremely limited by 1999 standards. Its "fixed" memory -- what we now call ROM -- held approximately 72,000 bytes, about one-twentieth the storage capacity of one 3.5-inch floppy disk today. Its total random-access memory (RAM) was about 4K; the average home PC now comes with 8,000 times more. The limitations of the equip-ment would become dramatically apparent during the lunar landing. Data overloading caused several computer alarms that turned out to be worrisome, but not critical.

* Summer Road Trip?

If your car got 10 miles to the gallon, it could travel around Earth about 400 times on the same volume of fuel expended in the Saturn V launch. All of that was required to reach Earth's surface "escape velocity" of about 7 miles per second, the speed at which the rocket could shake off the planet's gravitational hold, and put the spacecraft on course to the moon. Thereafter, mission navigation was conducted with comparatively small bursts from the Command and Service Module's main engine or the lunar lander's rockets. In all, the astronauts traveled more than half a million miles.

* A New Kind of Freedom

The Saturn V launcher with Apollo spacecraft stood 60 feet higher than Statue of Liberty on its pedestal and weighed 15 times as much as the statue. The Saturn V used for the Apollo 11 mission was the sixth of its kind. The models I and IB, which had been tested in unmanned flights from 1961 to 1966, were much smaller. In fact, the first stage alone of the Saturn V, which debuted in November 1967, was taller than the entire IB employed in the first successful piloted Apollo mission (number 7).

* For more information on Apollo 11 and related missions, a good place to begin is NASA's online anniversary Web site at http://www.hq.nasa.

gov/office/pao/History/ap11ann, which incorporates dozens of color images and numerous links to other Web pages. Other Internet sources include the Smithsonian Institution's Air and Space Museum at http://www.nasm.edu:80/APOLLO The Apollo 11 Command Module is on display at the museum. In Rosslyn, the Newseum has a modest exhibit on world press coverage of Apollo and space travel in general. (See http://www.newseum.org/dateline -- moon.) In print, one of the most complete and accessible popular accounts is Andrew L. Chaikin's "A Man on the Moon: The Voyages of the Apollo Astronauts" (1994). Michael Collins described his experiences in "Carrying the Fire: An Astronaut's Journeys" (1974), and Buzz Aldrin wrote "Men from Earth" (1989) with Malcolm McConnell.

CAPTION: Flight controllers monitor the Lunar Module as it descends toward its landing site on the moon.

CAPTION: Edwin E. "Buzz" Aldrin Jr. walks on the moon. Reflected in his visor are the lunar lander and Neil A. Armstrong, the mission commander who took this photograph. Below, a Saturn V rocket launches the mission.