Jimmy Carter, the 39th President of the United States, is one of America's most sports-minded leaders. Yet, this hardly seems unusual considering that he grew up on a 4,000-acre farm additionally equipped with a tennis court, baseball diamond, pole-vaulting pit and swimming pool, plus all the space and good Old South climate that the little town of Plains, Georgia, could muster.

In case you're thinking that the sporting surroundings of the four Carter children were plush and luxurious, it should be pointed out that the farm was a hardworking one; the tennis court of crude dirt; the baseball diamond and vaulting pit dug by hand and cleared by Jimmy himself; and the "pool", a 4' x 12' dammed-up creek, stocked with crawfish.

According to "Mizz" Lillian, son Jimmy was small for his age and did not reach full height until the 12th grade. "Still", she said, "this did not deter him from playing any sport, even basketball. He also had flat feet and when he got his appointment to Annapolis he determinedly sat for hours rolling his bare feet on a Coca-Cola bottle until he created an arch."

As President, Mr. Carter continues to find pleasure in sport and seeks time out from the heavy duties of his office by being physically active. Pictures of the President in sawed-off blue jeans, tee-shirt and sneakers are not uncommon. One of his favorite games is soft-ball. A one-time fielder in his youth, the President usually pitches in the pick-up games he inspires.

He still loves to fish, though he and Rosalynn prefer an early morning deep- sea jaunt from the beach at St. Simon's Isle to the old way of muddying up the backyard creek for a catch of crawfish. On a given weekend at the Carter's mountain hideaway in Thurmond, Md., the President has been known to play a set of tennis, practice hitting balls against a backboard, and wind up with several miles of bicycle riding.

Quail hunting is another-away-from Washington pursuit and on one occasion he joined Amy and her playmates in practicing target shooting from his mother-in-law's backyard in Plains.

JAMES EARL CARTER Born Oct. 1, 1924, Plains, Ga.

Photo: Jimmy is a hitting pitcher