YOU SHOULD be naked, as a rule, before plunging into the great fountain basin of the Tuileries Garden. The water there is none too clean, and it stains white flannels and ruins your passport.

But on that day there was no time for getting back to nature. There was obly time for American culture and honor to operate in a flash.

Our topic today is, as you will have guessed, the nature of heroism, and the nature of cowardice also. This account is from my uncompleted book, "Hank's Guide to the Heroic Life." And now back to the facts:

The sun was soft and the sycamores shivered deliciously on that summerday, and our hero-to-be was proceeding across the Tuileries to meet a Scotch girl.

She was staying at the Hotel Wagram on the Rue de Rivoli, not far from the great monumnetal stairs leading out of these famous gardens.

Our hero was in his early 20s and was sauntering through the trees like a unicorn crowned with roses because, as he reflected at the time, he looked pretty damn good and his white flannels were decent in the waist but tight enough around his legs to show off his calf muscles, the reward of some years of running about on track teams.

He approached the great basin, with 200 Parisians sitting on little chairs fanning themselves against the frightful heat. It was 82 degrees and the French, in that summer of 1947, enjoyed falling unconscious from the heat on every sidewalk.

On the foot-wide rim of the basin a baby sat, aged five months perhaps, with his teen-aged sister standing on the ground, her body touching the raised basin and the baby.

The baby started to crawl-his first crawl, most likely, and almost his last-and fell in and went down like a rock. You would think babies would float a little, being puffy, but this one went down as if shot.

The young woman gazed. Her eyes were fixed on the creature under water. For the longest kind of time she stood there-maybe three whole seconds-and said nothing, screamed nothing, did nothing.

The people in the chairs kept on fanning themselves, looking idly about. Most of them did not see the baby, and the ones who did see him assumed his sister would simply reach in and fish him out.

Our American hero, roused from his continuing reveries on his sharp appearance, sprang.

He was 80 feet from the basin, but he alone was on his feet and had a perspective of the baby falling in, and he alone perceived the young woman was unable to budge. Like a story people really can freeze.

"I am going to look like an ass," he thought as he began his sprint. No second is too split for a young man to think about himself.

Into the basin he leapt. The baby was on the bottom, not moving. Our hero fetched him up, set him on the rim, and the sister came to life and began to cry, snatching the baby to her arms.

By this time the people on the chairs were roused and all began to talk. "Alors," they said, with that splendid French intonation of alarm and contentment at once.

Down the monumental stairs, once it was all over, came France's finest, their uniforms touched with scarlet, and all of them blowing whistles and prepared to quell whatever the riot was.

Our hero climbed out of the basin looking, as he had foreseen, like an utter ass, the water cozing from his shoes and his white flannels not only stained but reeking like a sheep fetched out of a thuderstorm.

He took the subway home. His fellow passengers withdrew from him as much as possible. He wanted to say:

"You prissy jerks. I have just saved a citizen of France at enormous risk."

Instead he just got off at St. Phillippe de Roule and earned a fishy look from his concierge.

His flannels were the sort no longer made, a quarter-inch thick. A youth could be a real slob, but in flannels like that he looked like something.

The Scotch girl, who for some reason had been unwilling in previous days to have a date with our hero, had of course succumbed to persistent urging, and the flannels were the item calculated to end all resistance once and for all. And they would have, too.

Well. He got dressed again, took the subway back, crossed the Tuileries Gardens once more and the Scotch girl flat refused to see him, after her two-hour wait, and would never enen talk to him on the phone.

To say nothing of the cleaning bill, and the commotion of the passport. Our hero was to leave the next day for Geneva, and his passport was sopping and all the ink had run and the little sticker came off.

This is no good," said the Swiss at their Paris office.

"The American Embassy says it's okay," our hero lied.

"Well, it's not," said the Swiss, "but if your government wants to recognize a ruined passport it's no skin off my nose," and he glued in a Swiss sticker.

At the American Embassy the man said:

"This is no good."

"Well," he said, "the Swiss think it is, and they've put their sticker on it. If it's good enough for them why isn't it good enough for my own country?"

So he said well all right, and made some magic marks and the prince went right along with a passport full of run ink, water-stained pages and vanished stamp.

One reward of heroism, in some cases, is a dazzling insight into how governments work.

But our hero, back to him, thought a lot about why nobody else did anything, though they were closer. And the answer is clear:

They did not think there was any danger.

There was no noise, no screaming. The sycamore leaves shivered as usual, and the cherries in the paper cones were being dutifully plopped into the mouths of those sitting near the basin.

And just as our hero thought of his flannels, the Parisians were thinking of similar things. I do not doubt that more than one inner conversation went like this:

"There is a baby in the water. Someone must pull it out. Many can do so. I, on the other hand, have to catch a bus in five mintues."

Things are not presented to us as moments of enormous crisis. Dogs continue to race about on the grass. Pigeons keep doing their necks. The old lady keeps on poking at her lemon ice with an inadequate spoon. So how is one to know that now is the time to act?

And who can seriously believe the difference between life and death amounts merely to some undignified act like jumping in a basin of water and ruining your flannels?

If a house is afire, one might brave the flames to save a baby. In such a case one would know that bravery was called for, and that every second counted.

But on a summer day, in the gardens of the Tuileries, one had no such clues.

My Observation of years is that men will risk death, when the case is clear.

They will not, as a rule, risk getting their pants wet or making a jackass of themselves in public.

There was that case in New York, where a young woman was murdered on the sidewalk and nobody did anything. All anybody had to do was pick up the phone and call the cops.

Exactly. It was because so little was required, and because so many hundreds could have done it, that nobody thought of doing it himself.

There was no callouness there, no fear of being involved. What, after all, was there to fear?

The ordinariness of doom, I suspect, is what threw everybody off. Those same bystanders, given clearer clues, would have risked life itself for her.

No man is a hero while brushing his teeth or clipping hair out of his ears. He needs some kind of warning that this is the moment to act. He has to be in a position of dignity. He has to be sure everything's zipped.

Life does not always give that warning. The dogs still trotting about sniffing the trees. A day like any other day. How could he know?

Then there is normal fear. Our hero in the water basin did not have to face that. But fear is normal, and a man needs a minute to deal with it before he goes past it.And oftern life does not give him that necessary minute, and he wonders the rest of his life if he is a born coward.

Usually he is merely a guy who needed a minute more than he got. And the gungest-ho heroes can behave poorly if they are caught off guard.

Next year we shall deal with another sort of hero:

The jerk, say, who is scared of dogs but behaves brilliantly anyway. And the one that can't take loud noises, but gets on with it all the same. And the one who is sort of at the bottom of the totem pole, as far as respect and stroking are concerned, but who does not accept the case of Scotch anyway. Not because it's beneath his dignity-nothing is, the world would think-but because he is on his way up and is reaching for virtues he does not yet have.

Courage over the long run is something different from our fine hero of the fountain basin. Tune in next year.