When the moment finally arrived, 3.98 seconds late the second time around, 20 years to the day after Soviet cosmonaut Yuri Gagarin started it all, John W. Young's heart rate crept up to 85 beats a minute. Robert L. Crippen's soared to 130.

Jubilant U.S. space officials joked about that, saying that Young, the veteran astronaut, had been through all this before and Crippen, the rookie, had not. "Next time Crippen will be that cool, too," said George Page, launch operations director for the space shuttle Columbia, which had just rocketed into reality.

Young, indeed, had gone through this before -- sensing the lightning spark igniting 4 million pounds of fuel next to him, feeling the sudden power of almost 50 million perfectly harnessed horses pulling at him, yielding one last time to a persistent Earth gravity three times normal, passing through the buffeting phenomenon known as Max Q and then escaping into the liberation of weightlessness.

Still, the more important question -- not asked here at the Kennedy Space Center or in the nerve center at Houston -- was about the American heartbeat, was it racing now? Will it cool down, like Crippen's the next time around -- and the next, as the shuttle becomes as commonplace as its name?

"Through you, today, we all feel as giants once again," President Reagan, whose favorite television show as governor of California was "Mission Impossible," said to the two astronauts. The president, who was just released from the hospital on Saturday, awoke 10 minutes before the launch was scheduled to watch the lift-off.

Until this morning it had been six years since the reality of an American manned space flight.

They have been strange years. Missions impossible -- the cinematic surreality of "Star Wars" in Dolby sound and the 25-cent kicks of "Space Invaders" on barroom computer screens -- have consumed American fantasies. The reality of billions of dollars for the pedestrian beginnings of the authentic article has been less appealing.

Fantasy and reality tend to merge in American mass media -- docudramas using truth to approach fiction, pure drama using fiction to approach truth until modern news is just a shade off modern fiction, reality often fading into a twilight zone of take your choice.

It wasn't different to determine the reality at Pad 39A today. That small percentage of Americans who were here not only saw and heard it, but they also felt it kick them in the chest.

Columbia left earth, those scant 3.98 seconds late, in a litany of thunder, light and sound, the sun-orange flames of its rockets licking out to sear the pad and nearby palmetto scrub. But it was the sound that drove home the reality.

It poured slowly across the barren flats and soupy waters of Mosquito Legoon, moving in invisible rivulets toward the nearest observers three miles away. Then it struck, as the rocket already was lifting rapidly away, in a thump-thump-thump staccato that shook viewing stands and pounded into the chest as well as the ears.

A column of gray smoke, rolling like the plume that emerged from volcanic Mount St. Helens a year ago, trailed the 48 million-horsepower solid fuel boosters, leaving an eerie shadow against the almost cloudless sky.

Hollywood couldn't reproduce that.

Still, as the spaceship moved through Max Q -- the moment of ultimate stress 52 seconds after launch which may have been what tore a handful of heat tiles off Columbia -- and on into its routine test pilot's mission, it was difficult to tell if real life could keep up with the attractiveness of fiction.

The first wobbly TV pictures came back from space, hardly widescreen cinematography, hardly accompanied by Dolby sound. They were gray and indistinct, fuzzy and as bland as the test pilot's lingo on this test pilot's trip.

Ironically, it was the televised panning across the missing tiles -- a nice scriptwriter's touch adding fiction's dramatic requirement of unexpected danger -- that may keep Columbia in the twilight zone of American acceptance.

Otherwise, the mission, so far, would have been almost too flawless to make good mass media fare.

And it's the masses now who will decide how far and how fast the United States will go in mankind's inevitable reach for the stars.

One commentator offered the thought this week that the United States was running the risk of becoming the Portugal of space -- the nation reached out first for the New World, found it, found no instant spices or gold, and left the alien void to adventuers from other countries.

So the real test is in America's heartbeat now. The space shuttle will, indeed, become dull fare in the future -- a bus ride that will be no match for the galactic collisions of Hollywood or Bally computer toys, no match, even, for the moon walks of a decade ago.

Astronaut John Young went to the moon the last time he left Pad 39A. Being human, his heart raced faster then. This time he will get just one two-thousandths of the way there. The voyage of the Columbia is a mission impossible of its own. But whether it makes Americans "feel as giants once again" or turns them back to the easier escape of "Space Invaders" will tell more about the future than all the instalments of "Star Wars."