The last time Jimmy Carter was here, a three-hour stop in May, someone asked him whether he thought his hometown had changed since he became President. No, he said, he was pleased that Plains had not changed at all.

Even coming from a man who has promised never to tell a lie, that statement, it could safely be said, was something less than the whole truth.

Plains, of course, began to change as soon as Carter became a serious presidential contender. With his nomination, then election and finally assumption of the presidency, the process accelerated, so that now this once sleepy south Georgia hamlet is dotted with tacky souvenir shops, its streets clogged with tour vehicles.

But even if the Plains he knew is gone forever, Carter is acting during this five-day vacation like a man who is very much at home. His days have been filled with the simple activities he seems to enjoy so much and which shaped his life before he began his drive for political power.

There was church on Sunday and later that day a family reunion, filled with Southern-cooked food and talk of times past. There was a visit to the Carte peanut warehouse to see his brother, Billy, and breakfast this morning at the pond house with his mother, Miss Lillian.

On Monday afternoon, Carter, as any farmer would, traveled into the countryside to inspect some of his lands. It is one thing for a President to read reports about the drought that has devastated crops throughout the nation; it is another for a farmer to stand under a burning Georgia sun and see the effects firsthand.

For the reporters covering Carter, many of whom spent much of last year here and vowed never to return, this trip to Plains has been filled with nostalgia. Carter remains an unpridictable man, especially on his home turf, but the second day here he promised to give 30 minutes notice to the press before going anywhere.

When he does go, the White House press office staff hangs a red blanket from the balcony of the Best Western motel in Americus, the signal for the reporters for the wire services and the television crews to scramble for the 10-mile drive to Plains.

There has been little need to scramble here, and little else to do. It is as hot as it is in Washington, and almost as humid, but the air is clean.

And in the later afternoon stretching into evening, there is the all-consuming passion for softball. It was last summer that reporters noted that Carter's fiercely competitive instincts did not leave him when he took to the softball field. That much has not changed during summer in Plains.

The first game was Sunday night, the President pitching for the White House staff, Billy Carter for the press corps. It was a game marked by several disputes over contested calls, all but one of which were won by the White House. And it ended surprisingly, the press winning, 14 to 11 in 10 innings.

A rematch was demanded for Monday, and from the beginning it was clear this was serious business. Real bases were in place on the field, replacing the cardboard and sacks on Sunday. The base paths were lined with chalk. Three young men from Georgia Southwestern were recruited as umpires and they announced at the start that any arguing or cursing would mean immediate ejection from the game.

The White House brought a ringer, a 6-foot-7 behemoth, Jim Braxton. He is White House press secretary Jody Powell's cousin, Sells life insurance for a living and once was a successful minor-league pitcher. The press corps dubbed him "Big Foot."

The reporters brought their own ringer, whose first name was Dave and whose last name remained unknown. He works for Billy Carter at the Carter peanut warehouse and, the President said during the game, was once considered the finest baseball player in all of Sumter County, where they take their baseball seriously.

Braxton slammed two home runs over the fence in left field and his play in the outfield sparkled. But Dave the Ringer hit three home runs and played with big league style at shortstop. The press won again, 11 to 9.

There is another softball game scheduled tonight. it is being said that the whole contingent press corps, white House staff, Secret Service and President - will not leave Plains this summer until Carter wins one.