The tallest of the "Too Tall Kearneys" was always built for basketball. He was six feet tall in the seventh grade. By the time he reached high school, most doorways were a threat.

But until this year, after 21-year-old Steve Kearney finally stopped growing at a quarter inch past seven feet, he only looked the part.

"I was terrible, uncoordinated and . . . awkward," says Steve, who is slightly more candid about his past shortcomings than the rest of his family.

"He never had much talent," admits Gene Kearney, Steve's father and loyal fan during a less than illustrious high school basketball career at Fairfax County's George Marshall High School. "In fact, he was rotten."

The Kearneys allow themselves to rate Steve's past performances with such honesty only because of his present transformation. After years of painful, and seemingly fruitless persistence, Steve has become a basketball player.

"I don't know how he stuck with it," says his father, with a pride that early bloomers never hear. "He just kept it up and worked his tail off."

Steve will not make anybody's college All-American team this year, but he is starting for the varsity at St. Joseph's College in Philadelphia, a school that does not take basketball lightly. And his rate of improvement has been so rapid, he is now thinking of playing professionally after college, maybe in a European league.

"I've got all the tools to be as good as I want," says Kearney, who seems shy and vulnerable until he begins talking about his transformation from ugly duckling to slam-dunking swan. "All I have to work on now is my confidence."

Being tall and terrible is rough on the self image, admits Kearney, especially in a family that is mosty tall and talented. Steve is the oldest of six Kearney children and all of them go to the hoop.

Little brother Tim, a 6-foot-11 senior at Marshall High School, is everything Steve's coaches hoped he would be. Tim has already gotten 200 letters from college scouts eager to recruit him.

Linda, a 5-foot-11 freshman at Potomac State College in West Virginia, and Suzanne, a 6-foot-1 freshman at Marshall High School, are both playing for their varsity teams.

There is no team at Longfellow Elementary School where 5-foot-6 Patrick is a seventh grader, so the 12-year-old plays for a Falls Church community center team. Six-year-old Adam is the runt of the family at 4-foot-11, but his mother warns there are tall days ahead.

"None of our kids seem to grow until the seventh or eighth grade," says Nancy Kearney. "Then they go up to bed one night at five feet and wake up the next morning at six. I'm not exaggerating."

Nancy Kearney accepts some responsibility for her children's size, since she is 5-10. But she blames her 6-foot-6 husband for the children's obsession with bouncing balls.

"I never had any real interest in sports. I still don't except for basketball," she says. She has, however, become something of an expert on basic sportswear. "All I seem to do is wash gym shorts and socks."

Gene Kearney is a computer salesman whose only hobby is watching his children play sports. This year he and his wife will be commuting to games in three states. Next year it could be four.

The Kearneys, who allowed themselves to be tagged "Too Tall" years before it became popular with NFL football players, say being heads above the crowd creates its own kind of problems. Linda and Suzanne complain that the number of boys who are tall enough to feel comfortable dating them are uncomfortably few. Steve and Tim get most of the stares and the inevitable puns.

"When people ask me how's the weather up there, sometimes I feel like spitting on their shoes and saying it's raining," says Steve.

Gene and Nancy Kearney say they have their own sacrifices to make. Ask about the food bill and he catches his breath. Talk about the cost of shoes, and she puts her forehead in her hands.

"If we had known they were going to be so big, we wouldn't have had so many," jokes Nancy Kearney. "They were such cute little babies."

Steve has suffered the most because of his size. From the time he was tall enough to attract the attention of a sports-minded world, he has been told basketball should be his game. Until now, it wasn't. But he could not avoid the challenge to succeed or the feeling that anything less was failure.

"I got a lot of abuse," says Steve gently. When he talks about being a "flamingo" on the basketball court or running at night "so nobody would see how awkward I was," it is with a smile. The only time his face grows dark is when he remembers a ninth grade coach in Omaha.

"He told me I'd never make another basketball team as long as I lived," says Steve. The worst part of that memory is that he believed it was true.

Now, says Steve, the residue of those past failures will only make the taste of success more sweet.