When the ball left Kent Hrbek's bat and soared toward the right field wall Tuesday night, fans leaped to their feet to see if the rookie's hit would clear the fence.

Would this 21-year-old, who grew up looking out his bedroom window at the lights of Bloomington's Metropolitan Stadium, then home of the Minnesota Twins, have his ninth home run of the season?

Would the Twins' first baseman, leading the American League in total bases, extend his hitting streak to 22 games, only four off the modern record for a rookie?

One man could not jump to his feet to watch the ball--Ed Hrbek, the rookie's father.

Last August, when the Twins first called up the kid from Visalia in the Class A California League, Ed Hrbek, 52, could still bounce up and cheer, could still walk down to the clubhouse to fraternize with his son, the major leaguer.

Now, the father can't speak; he writes his thoughts and his answers to questions. Now, Ed Hrbek and his wife Tina sit in the last row of seats behind home plate in the new Metrodome so that Ed can put his long legs over the seat in front of him. Nobody sits in front of the Hrbeks or blocks their view.

The Hrbeks found out a year ago that Ed was suffering from Lou Gehrig's disease; they learned last May that the tall, dignified man with a touch of gray in the temples and the grace of a natural athlete had amyotrophic lateral sclerosis (ALS), cause and cure unknown. The disease causes the lateral columns of the spinal cord to harden and muscles to atrophy.

"Why him?" was all that Kent says he kept thinking then, pitying himself.

But, slowly, as the father grew weaker, the son found strength. At first, he wanted to come home from the minors. But his dad ordered him: "You stay and play . . . Don't let me spoil what you're doing."

So, the son, who hit only .203 and .267 in his first two years in the lowest minors, stayed. And he played, batting .379--the highest average in all of organized baseball. Kent had always wanted to play in the majors, ever since he'd been his father's bat boy in the park beside their house in Bloomington.

But now the timetable was more crucial. Lou Gehrig died at 37, two years after the disease was diagnosed. Some live 10 years with the disease. "I know he's dying," says Hrbek, "but they can't say when."

When the phone call came to Visalia Recreation Park last Aug. 24, Hrbek was ready for the ridiculous jump from the Class A to the majors in a day. Hrbek flew to catch the club that same night in Yankee Stadium, even hastily signing papers for the Twins without realizing, he now says, that he was agreeing to play for the major league minimum salary ($33,500) for 1981 and '82.

That night, in Gehrig's park, the 6-foot-4, 215-pounder stepped up in the 12th inning, score tied. The game was on TV back home. By the time his fly ball landed, it was in the bleachers; Hrbek had won the first major league game he'd ever played in with a home run.

Hrbek, who wasn't picked by the Twins until the 17th round of the 1978 draft and who had to win a five-way fight for the first base job this year in spring training, hasn't stopped since.

In the first 19 days of the season, he hit eight home runs--all but one at home with his parents in the stands. The other was on TV. "Seen them all," wrote Ed Hrbek on his pad. Then, as pitchers started skirting his power, Hrbek adjusted, hitting to all fields, starting his current streak, now at 23 games. At midweek, he was batting .315 and had a .629 slugging average.

"If you'd told me a year ago that my dad would be dying and that I'd be trying to play in the major leagues at the same time, I'd have said, 'Well, I couldn't handle nothin' like that,' " said Hrbek Tuesday night. "But I'm handling it better than I ever thought I could . . .

"If my mom and dad can handle it, I oughta be able to. We all felt sorry at first, but now we just act like there's no change. Mom'll get all over him sometimes and yell at him. He'll pat me on the back and it's a great feeling. But if I strike out, he'll be all over me about chasing a bad pitch."

Hrbek is a handsome, brown-haired lad who will turn 22 next Friday. He continued to live at home until this month, when he and teammate Gary Gaetti rented a house, in part so Kent could get out of his mother's way.

"This is the lowest part of my life and the highest, all together . . . and it's the same for him . . .

"I was talking to one of the Red Sox tonight. His father is dying of cancer. We were saying it's the same for both of us. You pray and hope . . . but, at least, I can go out and show him what I can do up here . . . Because he loves to watch the game so much, I can give him some pleasure every day."

As Hrbek came to the plate in the fourth inning Tuesday, his parents and Ed's brother, Jim, were reminiscing. "I remember when they'd all go up to Bemidji for a week's fishing vacation," says Jim, "but if Kent had a baseball game when he was 8-9-10, they'd drive 200 miles each way so he could play and they could watch . . . Ask his father how he used to coach him."

"I coached for two or three years," writes Ed Hrbek. "Not now, any more." He smiles sheepishly.

Others make easy predictions of greatness that can't help a rookie, especially one who, until the last year, was known mostly for his excellent glove and deceptively good speed. Manager Billy Gardner says, "Triple crown potential." The Twins, desperate for attendance, are milking hard. Above Hrbek's locker is a poster of his hero, Ted Williams; the Twins already have authorized a poster of Hrbek.

The fame is, already, a bit of a pain. "Because I grew up here, everybody wants a little piece of me," says Hrbek. "I need some time for myself."

"The phone never stops," says his mother. "We've got new relatives we never heard of coming out of the woodwork."

Hrbek's father holds up a finger to disagree. "He's handled it real good," writes the former power company supervisor.

Even on the field, Hrbek has had plenty to handle. One by one, all the little aggravations that unhinge rookies have beset him. Always prone to muscle pulls, he has had a sore back and a taped wrist that had stopped his homer production since April 25.

This night, as Boston's Dennis Eckersley prepares to pitch, Hrbek hasn't had a homer in 16 days. "He got two (homers) off Eck in spring training," writes the father hopefully.

Eckersley tries to throw a fast ball on the fists, but Hrbek's bat is too quick. Although the ball strikes near the label, still it drives right fielder Evans to the fence. As the ball flies, Tina Hrbek stands up, protectively making sure that no fan moves into her seated husband's line of sight.

Evans jumps, but it's gone, a home run.

As Hrbek slowly circles the bases, his father's eyes water. So do his mother's. But they don't cry. This isn't crying time. The parents get those about-to-burst smiles on their faces that every child who ever did anything right has seen.

"He could have played any sport he wanted to," writes the father proudly. Then he has second thoughts. He writes again: "Don't make it sound like we're boasting."

What does this moment feel like, the father is asked.

Slowly he raises his hand far above his head; then, as though he were popping the cork of a champagne bottle, Ed Hrbek fires his thumb straight up in the air.