Instead of boozing it up with the boys on his last night of freedom, the prince of Wales spent his wedding eve in Hydy Park with 400,000 other Britons watching fireworks.

"They're crazy," said a partially hysterical cab driver tooling down Sloane Street when he heard the crowd estimate. "I know crowds when I see them. They was a million."

"Glorious," cried a man when one of the multitude of three-stage sky rockets died in a fiery confetti of trembling gold.

"Send up a big one, mate," hollered a gentleman of enthusiastic lungs and substandard vowels, but his prayer was heard and a whopper was fired up back of the specially constructed wedding cake stage-set palace that workmen have been erecting for some days now.

"It's so long since we've had anything," said Isobel Ward, who works in a London dress shop, and she was right, of course: The last time fireworks quite like this were seen in London was in 1749, when King George II warmed up this northern sky with 50,000 pounds of colored gunpowder. That grand night marked the end of the war of the Spanish succession.

But it's not wars, as all London knows, that bring on the fireworks, but royal marriages. The first Queen Elizabeth, who did not bother with a mere man but rather married the people of England, nevertheless gratified the capital with her fondness for "shuyting of gunnes and fire round about," and this fondness was clearly shared by the present Queen Elizabeth tonight. She often threw her head back, smiled and laughed heartily with Prince Charles as the elaborate set pieces blazed. Some showed the emblems associated with the prince, others were waterfalls of blazing silver, and a tremendous whirling pinwheel sun started gold and turned to silver, flinging trains of sparks in a thousand directions for 50 feet.

Nancy Reagan, wife of the president, sat with heads of state behind the royal family, and she seemed delighted with the entertainment.

The display lasted 22 minutes, except for a four-minute interval, during which the computer setting off the fireworks presumably went out for a beer. The fireworks cost about $130,000, raised by the sale of television rights.

"The music is what made it," bubbled an enthusiastic American woman who had a seat near the royal enclosure.

"Ow, we're not hearing the Orpheus choir," wailed a woman in the great mass of folk packed into the park who heard nothing more than an occasional puff, puff, thought to be the ceremonial cannon firing salutes, and an occasional tick, tick, like a very soft heartbeat, presumed to be Handel's gorgeous "Fireworks Music" or else some of the numerous bands and choirs.

"Nobody could believe the queen was 11 minutes late in arriving," said a guest in the royal enclousure, "because of the traffic."

For events such as these the queen is on time, period. But to the hundreds of thousands in the park, it was believable enough.

Two hours before the spectacle began there were whold football fields of people streaming through Marble Arch and other entrances. The sidewalks for a mile around the park were packed with people seven abreast, marching to Zion.

A man on a motorcycly wore a Union Jack mantle that streamed back of him, or would have, if his motorcycle had moved facter than a turtle.

Vendors sold programs. "Signed by Prince Charles himself at the palace last night," cried one of them, though he sold no more than the rest. Lies get you nowhere.

The crowd might have been even more fabulous except that already, 15 hours before the 11 a.m. wedding in St. Paul's crowds had begun to line the route from the palace to the cathedral.

An astonishing number of babies and children still in buggies were poking about in the crowds, barking people's shins, and the common English "sorry, sorry," was uttered an estimated 4 trillion times during the evening.

"Please come out of the trees. You must come out of the tree," said a dome-headed London bobby to a youth high in a birch.

But later the stately trees of Hyde Park blossomed with youths more plentiful, perhaps, then the cops. Ambulances prowled about, giving off mournful wails as they moved slowly among the hale and hearty.

No protests were heard, no royal raspberries, and the cheers greeting the prince and his parents were all but deafening as they rode into the park to begin the festivity.

After that, everybody beyond a certain road was asked to leave the park and view the scene from some street outside. Instead, they crossed the road at the first opportunity and as tens of thousands funneled into a narrow passage, a few women were unduly squeezed.

"Stop it. Oh, do stop it," moaned one, and her plaint was echoed in various pitches, with varying degrees of genuine alarm, by numerous others.

"I do not wish to be helped along in that way," said one woman, more in indignation than fear.

Six uniformed police within 15 feet of roadway were seen.

Once the lemmings crossed the road, they thickened the already dense crowd neareer the royal family. Fathers holding kids on their shoulders were seen every four feet, then every two feet.

"Michelle, don't you move one inch," one mother ordered for two hours straight, and Michelle, needless to say, obeyed since there was no place for her to move to.

An unsightly object labeled Snack Bar was conveniently stationed between 20,000 viewers and the fireworks palace.

Never has such gallantry been seen, however. An estimated 100,000 young men insisted on hoisting 100,000 young women in their arms. They did this repeatedly. Chivalry is alive and well in London.

The day had been beastly and gorgeously hot by London standards, and this always inspired the young to take off shirts and as much pantaloonage as the law allows, but in honor of the state occasion, all the shirts and pants were on again by nightfall.

As the show ended, the vast audience clapped. Then everyone on the west side headed east and all on the east side headed west. Endless good humor was everywhere. An American was among thousands climbing the spiked iron fence of the park to get out. He was temporarily detained by the spike and his blue jeans suffered slight damage, but he got a cheer when he freed himself and vaulted over. He then made a cup of his hands, stuck them through the iron bars and an elegant small lady of Iran put her dainty foot therein and wobbled over.

"Ah, my shoe," she said sadly.

"Never fear, never fear."

She got her shoe back on in the fullness of time, and her little daughter was then hoisted over the fence with international cooperation from both sides of the barrier.

For an hour all traffic was at cross purposes. The calm and happy muddling about -- a most dangerous chaos in almost any city but London -- was not helped by the custom of some London lovers. They lie down on pink quilts on the park lawns, once the crowd thins enough to allow it, and the next hundred thousand people leaving the park go around them.

Bands of teen-age youths were beheld on the sidewalks singing "God Save the Queen," though not drunk. As American youth would surely be if bands of them sang "The Star-Spangled Banner" down the sidewalk.

Some walked about with open bottles of champagne and probably would have shared it if anyone had asked.

The prince, it was widely assumed and fervently hoped, went straight home, said his prayers and went to bed.

No such good report, alas, can be given for all other Londoners, some of whom appeared to be quite jolly well into the morning.

But then, as the shop lady said, it's been a long, long time between occasions of national festivity and joy.