Rufus (Bubba) Hadley, the well-spoken but ill-prepared United States marine, encountered reality tonight in the form of Teofilo Stevenson's right fist.

The great Cuban heavyweight measured the loquacious corporal for 90 seconds, flicking a few jabs, but only one thunderous right hand. Then, with his second serious punch of the evening - an invisible straight right - he mustered Hadley into a world he had never visited.

"Man, my head's still buzzing," said Hadley after being counted out at 1:39 of the first round. "My legs went stiff like somebody had said, 'Attention!'

"I told 'em, 'Legs, let's get it together.'

"But they said, 'Nah, we're not going nowhere'."

Stevenson, his alarmingly statuesque physique towering over the 6-foot-2, 205-pound Hadley, seemed mildly amused by one of his typical fights - that is to say, he never broke a sweat, threw perhaps a half-dozen jabs and two rights.

On an evening when Cuba's other demigod, Alberto Juantorena, finished second in the 400 meters, losing to Tony Darden of the U.S. in a blazing 45.08, fastest time of the year, Stevenson easily maintained his island's honor.

Hadley handed Stevenson a U.S. flag that he carried in his sock before the fight. After the "boute," Stevenson reciprocated by lifting Hadley in his arms like a baby and carrying him back to his corner after Hadley had wobbled over to the Cuban's corner to shake hands.

"If I'd have known what hit me, it wouldn't have hit me," said the 18-year-old Hadley. "It's the ones you never see that get you."

"He hit me in my ear drum . . . it feels crazy, man. I never felt like that before. It threw me all off balance. It was a good thing the fight was stopped because even though I got back up, I was dizzy."

To Hadley's credit, he fought as he said he would when he predicted before the fight, "The gold medal is mine. I only have to go in and take it."

He tried his best to swarm at Stevenson and take the initiative - all it got him was one nice leaping sequence of three quick jabs to Stevenson's unmarked face.

"Hey, chalk it up to experience," said the chastened Hadley after his head began to clear and his left eye began to swell from Stevenson's two-by-four of a jab.

"I'm walkin' and talkin', just like I did when I came in here. My hands still work . . . see. I'll just have to work harder in the future."

Consolation came to Hadley from many quarters, one U.S. fighter pointing to the ear-temple and saying, "Bubba, the big boy just knows them vital spots."

"Stevenson has the fastest right hand in the history of boxing," muttered a U.S. coach in Hadley's still useful ear.

Perhaps the most disappointed folks in the tiny, packed sweathouse of a gym were the U.S. women's basketball players, who came in their "Bubba's Angels" T-shirts, carrying a huge Hadley banner.

As Stevenson's hand was being raised, the Angels filed out, raising the "No. 1" finger, hopefully referring to themselves. The crowd good-naturedly hooted at them as they left, laughing and giving them the mock thumbs-down sign.

Before the fight, Hadley had promised, "Stevenson will be beat . . . if you pinch his arm, what do you feel? Flesh, same as me, right?"

Tonight, Hadley got the same answer as 188 previous Stevenson victims - the Lightning Blow of the Caribbean is made of flesh, but his is harder and there's about 230 pounds of it.

Stevenson's victory was the only light moment of a bloody, raw evening in a Trujillo Alto Coliseum that qualifies as the pit beneath the nethermost pit and the hole hidden under the deepest black hole.

At the end of two nights of semifinal fights, the U.S. had placed six boxers in the Saturday finals, four of them winning tonight, while Cuba advanced five.

"After this week, Cuba won't be No. 1 in amateur boxing anymore," said stylish U.S. bantamweight Jackie Beard, who decisioned Cuba's Hector Lazaro. "It'll be the U.S. again. Cuba'll be lucky to take second place behind the Puerto Ricans, the way they're fighting for their home crowds.

With Beard's success and Lemuel Steeples' junior welterwight win over Cuban Joe Aguilar, the U.S. now owns a 6-2 edge in head-to-head bouts with Cuba.

Light heavyweight Tony Tucker and junior middleweight James Shuler also won tonight. CAPTION: Picture, Tony Darden hits the wire ahead of Alberto Juantorena. AP