Remember John LeBoutillier, the youngest member of Congress? He was the Republican representative from New York who called Sen. Daniel Patrick Moynihan (D-N.Y.) a "drunken bum," Sen. Charles Percy (R-Ill.) a "wimp" and Congress itself "a joke." Well, he won't be back next term.

Taking his place as the new youngest member of Congress is incoming Rep. Jim Cooper (D-Tenn.), a 28-year-old former Eagle Scout and Rhodes scholar who says, earnestly: "It's a privilege to know these guys. At this age, it's more than I ever dreamed of. I feel like I'm the luckiest person in the United States."

Cooper beat Cissy Baker, the daughter of Senate Majority Leader Howard Baker, in November. It was a race that got lots of attention, not least because it became known as a feud between two Tennessee political clans. Cooper says the press exaggerated, but you can't ignore the family trees: Cissy Baker is not only the daughter of Howard, but also the granddaughter of the late Senate Minority Leader, Everett M. Dirksen. Cooper is the grandson of the former speaker of the Tennessee House and the son of the late three-term Tennessee governor, Prentice Cooper.

Round one was in 1938, the year that Prentice Cooper first won the governorship--from Howard Baker Sr. The Coopers won round two, but not without some advice from the locals. As Cooper tells it, one day Cissy Baker, 26, cruised into a coffee shop in Sparta, Tenn., asked two codgers what they thought her chances were of going to Washington, and was told: "Pretty good. If you marry Jim Cooper."

"I was always getting comments like, 'Why don't you two just make babies?' " says Baker.

"Well," says Cooper, "those chances deteriorated after the primary."

Cooper is having lunch at 209 1/2 on Capitol Hill. He has dark hair, dark eyes and the serious air of a 45-year-old investment banker. He orders milk, but the waiter tells him they don't have any. "No milk?" he says. "You can't get milk at a restaurant here? Where am I?"

Cooper, a 1980 graduate of Harvard Law School, is not as naive as he might sound. Consider his undergraduate game plan at the University of North Carolina: "The first day of school, I knew I wanted to be either editor of the newspaper or student body president," he says. "Three years later, not four years later, I was editor of the newspaper--and a Rhodes scholar. I'm a serious-minded person, very goal-minded, very long-range."

"I can remember when we were in grammar school together," says John Cooper, his 26-year-old brother and campaign manager, "we were in a science fair. My project looked terrible. There was paint all over, and the names of the planets were crooked. But he'd built a little miniature computer, and it just looked great. The joints fit together perfectly. I asked him how he'd done it, and he said, 'It's just a question of how much you want it.' "

In Tennessee's newly created 4th Congressional District, a huge rural tract that is largely Democratic, Cooper won with 66 percent of the vote. Cissy Baker says it wasn't her year. "He ran a clean, aggressive campaign," she says.

"She clearly got beat up on," says Will Feltus, who did Baker's polling as a senior analyst with Robert Teeter's Market Opinion Research firm. "All along, she had a big negative we couldn't quite get to the bottom of. It was a combination of being her father's daughter, being a Republican and being a woman. Cooper, besides his age, didn't have any negatives. Although you could see how a southerner could be put off by him, because he's a snotty Harvard kid, he comes across good on the stump. I think it was easier for him to break into being a good old boy."

But in a year when the average unemployment in Tennessee was 16 percent, Cooper's Harvard background became less of an issue than Baker's proclaimed "foot in the door at the White House" -- a campaign tactic that backfired. Cooper, who ran against Reagan's record and spent some $700,000 to Baker's $1.1 million, is credited with never attacking her. This doesn't mean he didn't think about it.

"During the campaign, there was a Sigma Delta Chi tennis tournament," says John Seigenthaler, publisher of the Nashville Tennessean and editorial director of USA Today. "The governor Lamar Alexander and Cissy were on one side, and Jim and I were on the other. Well, Cissy's a real good tennis player. We were behind and really out of it. But Jim said to me: 'I'm not going to let this happen.' After that, he never hit a ball out." They tied, 6-6.

Cooper, who gave $380,000 to his campaign by mortgaging an inherited farm as collatoral for a loan, grew up in a large Victorian house in Shelbyville, population 12,000. His father, who was 59 when he was born, hadn't been governor since 1945. He's remembered as a tempestuous, rough-hewn politician, with none of the smooth edges of his son. One bit of lore has him riding in the back seat of his chauffeured car during the Depression. He saw the foreman of a road construction project sitting on a fence--and promptly fired him for sloth. The man cried, but the governor was firm. Or as one legislator at the time is said to have put it: "Prentice is the only man who could commit assault and battery just by shaking hands."

"We were scared of him," says Jim Cooper. "He had a hot temper. My grandfather had much more of an influence on me. I remember him saying to me, 'Look, if you lose your temper like that, bad things are going to happen to you.' I think -- I hope -- I'm much more like my grandfather. I get mad a lot, like my father, but not openly. There's never a reason to take your own personal feelings out on somebody."

Prentice Cooper, after serving as Harry Truman's ambassador to Peru, came back to run for the U.S. Senate in 1958. His son, who was 4, passed out cards that said "Vote for My Poppa." On election night, Poppa thought he'd won. He got in his car, made the hour-long drive from Shelbyville to Nashville, then stepped out to make his acceptance speech. But the car had no radio, which would have told him he'd lost--to Albert Gore Sr., the founder of another Tennessee dynasty. It is a well-remembered humiliation.

"One reason I like politics is because I saw so little of it," says Cooper, adding that his older brother, William, a Nashville lawyer, "was old enough to realize the impact on my father when he lost in '58."

Cooper went east to prep school at Groton. He liked North Carolina, but he really liked Harvard. "He loved law school," says his brother, John, with more than a hint of exasperation. "How many people do you know who loved law school?"

Interestingly, it was at Harvard that Cooper met an infrequent running partner--John LeBoutillier, who was in the business school at the time and who would later write "Harvard Hates America," a book about his disgust with the radical professors and students he encountered there.

"I don't like that book, and I don't like anything at all about John LeBoutillier that I can think of," says Cooper. "At school, he really seemed pretty normal. Clean-cut, pretty straight. Good runner. None of that resentment."

After graduating, Cooper briefly practiced law with a Nashville firm, but then jumped into the race when he discovered the new district included his hometown. A week later, he met Mimi Wallace, a Nashville stockbroker. They've been dating for a year and a half. "I was scared to death about the campaign most of the time," he says, "so I had to spend most of my time in the field. I like her. I just don't know her very well."

If he's at all scared about being in Congress at the age of 28, he's not about to let it show. "It's not a weakness, but a strength," he says. "I've had a lot of breaks in my life. It's time for me to return the favors."

Noblesse oblige?

"Sounds better if you don't give it a French name," he says. "1982 was just a great year. Once you win an election, once you've got the prize -- you're in the catbird's seat."

It's suggested that LeBoutillier, whatever his strengths or weaknesses, was less of a somber straight arrow.

"Yeah," says Cooper, pleasantly. "And he didn't get reelected."