Rosalynn Carter

Her idea of getting away from it all is standing knee-deep in a Georgia mountain stream, fly-fishing for trout. Or better yet, snagging steelheads off British Columbia's Queen Charlotte Islands.

''I caught an 11-pounder last week, and several that weighed 6 or 7 pounds,'' she says proudly, in a honeyed voice that sounds as if she'd be more at home serving pecan pies on lace doilies.

The team of agents in dark business suits and undisguised earphones who travel with her wherever she goes are a constant reminder of the eventful four years Rosalynn Carter spent in the White House. Although she was bitter at first about the Reagan victory that sent the Carters home to Plains, Ga., she now looks back on her time as First Lady with genuine fondness.

There's been talk of her running for state or national office, and she's eager to point out that she'll do ''whatever the candidate wants me to do'' in campaigning for the Democratic Party in the fall presidential elections. But for the present, Mrs. Carter is on the road to promote her own most recent accomplishment - a just-published autobiography titled ''First Lady from Plains.''

She writes in her book that interviews have always made her nervous, but as she relaxes in her hotel suite, Rosalynn Carter exudes graciousness and good ol' Georgia humor. In a wide-ranging conversation, she talks about her growing-up days in Plains, life in the White House, how she learned to deal with criticism, and the fun she's having at home today.

Her laugh is more of a girlish giggle, and it's easy to visualize her as the high school girl she writes of, squealing over Frank Sinatra and working part-time in a beauty parlor to help with expenses at home. At 17, she fell in love with the picture of the older brother of her best friend, Ruth, and she even walked out of a youth meeting at church to go to the movies with him on their first date. Within a year, she and Jimmy Carter were married.

A self-described ''stereotypical 1950s housewife,'' Mrs. Carter nevertheless talks about a marriage that was years ahead of its time in shared responsibilities. As a full-time partner in the Carter family peanut business, for example, she managed the books, kept track of which operations were most profitable, and always knew how much money was owed on debts. It was only natural, she says, for her to feel ''more a political partner than a political wife'' when Jimmy Carter ran for state, and then national, office.

In the White House, Mrs. Carter was often portrayed as an influential First Lady who did little to conceal her power behind the scenes. When she traveled to Latin America as special presidential envoy, testified on Capitol Hill on behalf of mental-health legislation, and sat in on Cabinet meetings, she came in for plenty of criticism. She's more reflective about the comments today, but her defensive antennas still crackle slightly when she is asked about the kind of influence she had with her husband.

''We talked together a lot about what we were doing,'' she says, ''but our relationship wasn't the kind that Jimmy would come home and say, 'What should I do about this?' That never happened.

''As for going to Latin America,'' she continues, ''the leaders I talked with there felt that I would take things back to Jimmy without going through the State Department or the National Security Council, which they had dealt with for years, and usually not in a very encouraging way. They were used to looking at the US as a big bully, I think.''

Mrs. Carter points out that Eleanor Roosevelt had set a precedent for testifying on Capitol Hill, and she says that at the Cabinet meetings she attended she always sat in the back of the room with the secretaries, adding crisply, ''and nobody minded a bit.'' When she was criticized for going to those meetings, she says, ''It could only be recognized as opponents trying to portray Jimmy as weak. That's all it was, pure and simple.''

If Jimmy Carter had a somewhat ''weak'' image in the press, the phrase that appears most often in news stories about Rosalynn is ''steel magnolia.'' Is it accurate, and if not, why does it linger?

She has a good laugh at that one, then explains somewhat cryptically, ''Once in print, always in print.''

It seems that, when she and Edna Langford, the mother of her daughter-in-law Judy, were on the road in Florida in the early days of the first presidential campaign, a reporter was assigned to follow them for a week. But after two days of getting up at 4:30 a.m. to watch them greet factory workers and staying up until midnight to cover speeches, the reporter had had enough. She returned to her home bureau and wrote a mostly complimentary story about the long hours that Mrs. Carter, a veritable ''steel magnolia,'' put in each day.

''I remember driving along with Edna when the story first appeared and laughing, and saying, 'Well, ''steel'' means tough and strong, and ''magnolia'' means Southern and genteel, so that's not too bad.'

''I knew how the phrase had originated, in the sense of a Southern lady working hard, but when it was picked up later on, I decided that a lot of reporters must write their stories by reading old newspaper clippings and using the same words over and over. By then I had also learned that you can either be defeated by criticism or you can decide not to worry about it.''

Like all proud mothers - and grandmothers - Mrs. Carter says she could spend an entire interview talking just about her family. She writes in her book that she asked her husband to add a passage to his Inaugural Address, indicating that strengthening the family would be one of the goals of his presidency, and she says that their time together in Washington ''broadened every member'' of their own family.

''Sometimes we were criticized for sending the children to represent the US at state funerals,'' she adds, ''but what people forget is how important it is for the first family to show an interest in the rest of the world. Everybody in the world, particularly in the third-world countries, wants to see the President of the United States - or any member of his family. It means so much to them.''

Now that her book is finished and plans are almost complete for the Carter Presidential Library and the Carter Center at Emory University, Rosalynn Carter says she's looking forward to getting more involved in community projects in Plains. But mostly, she's enjoying the time she now has to spend at home with her husband, children, and grandchildren.

''The other day a woman said to me, 'Mrs. Carter, isn't it kind of sad to see your husband . . . just building furniture?' and I had to laugh because she doesn't know how busy he is, or how he's enjoying what he's doing. It's really fun now, having Jimmy at home - just like it used to be when he was in the Navy. We run or ride bicycles or go fishing every afternoon. And last weekend, when we were at our cabin in the mountains, Jimmy caught some trout and cooked it for breakfast while I slept late.

''I tell you, it's really a wonderful life after the White House.''