So America's joy boys, John McEnroe and Jimmy Connors, will have at each other for the 19th time Sunday afternoon, precisely at 2 o'clock by Big Ben reckoning, and perhaps the Duke and Duchess of Kent should wear earmuffs against the imprecations of the aging brats. They also should have the butler tape the match on their Betamax, because this tennis will be wonderfully ferocious.

"If you're comparing us to Ali-Frazier," Connors said to a reporter who said Connors-McEnroe was the same sort of war, "that's probably the best compliment I could have. I play like Frazier. I put my face forward, let you hit it a few times, keep coming forward. He's like Ali, fluttering around the ring. He'll chip and slice, work it around."

And what does McEnroe think of that? "I haven't given it a helluva lot of thought," he said with brevity unknown to Ali.

"I've won some I shouldn't have, and he's won some he shouldn't have," Connors said of the series that stands 10-8 for him, including a straight-set victory two weeks ago on grass in London. "Every time we play there's something more in the match. It's my attitude against his attitude, his force against my force. I don't mean return of serve or serves or volleys. His inner drive against my inner drive. That's what it is."

"One thing I respect," McEnroe said, "is that Jimmy gives 100 percent. There'll be an intenseness because of our attitudes. What'll be seen tomorrow is what everyone might have hoped for. It doesn't mean it'll be 7-5 in the fifth, but it'll be a good match."

When last these gladiators met on the sacred sod of Centre Court, all England recoiled aghast at the goings-on. Connors, then newly a father, recognized in McEnroe the symptoms of diaper rash. A certain irritability preceded fits of squalling. So Connors did what any daddy would do.

Right there at Centre Court, in front of the Duke and Duchess of Kent and heaven knows how many other unemployed people, Connors swaggered to the net in his best gunslinger gait. Shaddup, he told the U.S. Open champion. And in case McEnroe didn't get the point of the discussion, Connors wagged a finger at him.

Naughty, naughty, Johnny.

McEnroe won that semifinal in four sets. Two months later, at the U.S. Open, McEnroe again beat Connors in the semis, winning, 7-6, in the fifth set. That Open meeting is memorable not only for the ferocity of tennis, but for Connors' symbolic work at the water jug.

At a change of ends, Connors had a mouth full of water.

He walked toward the other end.

He spat the water onto the ground.

Right at McEnroe's feet.

Perhaps it is unfair to open the dusty attic of memory and rustle about for instances where McEnroe and Connors have fallen beneath the standards of conduct expected from, say, long-haul truck drivers. For it is undeniably true that both are older now, and both cross their hearts and hope to die that they are wiser.

But . . .

Here is McEnroe's answer when asked if anything like these confrontations could happen in a Wimbledon final: "Uhhh . . . I'm not saying . . .uhhh . . . We get along better now . . . It's our attitudes . . . I would doubt it'd be anything like that, but, uhhh, we'll both be trying."

"We'll both be killing ourselves out there," Connors said.

Some dime-store shrinks hold that Connors sought out the inflammatory situations with McEnroe in 1980 because he felt his position eroding. From 1974 to 1979, he was the world's No. 1 player, holding the high ground longer than anyone ever. Then came the ice man from Sweden, Bjorn Borg, followed too soon for Connors' peace of mind by the flame thrower from New York, John McEnroe.

Connors beat McEnroe in four sets in the 1977 Wimbledon, the kid's first trip here, but by 1980 it was clear McEnroe would take up the hunt of Borg while Connors headed for the old folks' home.

From 1978 until today, Connors did not win a semifinal match in a Grand Slam tournament. This made him, the shrinks say, grumpy.

"I was in a bad mood that day, and so was he," Connors said of the 1980 Wimbledon. "That makes for excitement."

This time the tennis will do that. McEnroe won Wimbledon last summer. He also survived it. He conscientiously has avoided the major conflagrations he provoked a year ago.

Once all barbed wire and bombs, Connors at 29 is as sweet as a Wimbledon ginger honey yum-yum (25 cents a quarter-pound).

When he smacked an overhead 20 feet long today, a linesman made no call. Connors, in mock anger, waved an arm at the fellow and put his fingers an inch apart, as if to say, "This far out?"

The 14,000 customers at Centre Court loved the comedy. Not only that, in a great upset they have taken Connors as their sentimental favorite to win again the championship he won in 1974. At Court 1 the other night, the crowd began a soccer-stadium song for him.

"There's only one Jimmy Connors," they sang, over and over.

"I love it," Connors said.

"It's better than last year," McEnroe said of life this week.

Who will win? McEnroe has lost one set in a fortnight, Connors two. "If John doesn't serve better," said Tim Mayotte, McEnroe's semifinal victim, "then I think Jimmy will win . . . It'll be a mental game more than anything. If John isn't serving well, Jimmy will realize that from Point A. It'll be like a shark smelling blood. If either of them sense a weakness in the other, they'll attack it immediately."

It's the game's best server against the game's best returner of serve. Get the Betamax warmed up.