Luci Nugent was heading toward the iced tea in the White House yesterday and (after kissing a butler she recognized from the years she lived there) was asked if Lyndon Johnson was all that fond of trees.

"Yes. Nature in toto. You know how he loved the ranch - one day at the ranch was worth more to him than three weeks on tropic sands for the rest of us.

"People used to wonder - especially from urban centers - why it was he liked driving around on the same roads down there, and I can tell you it was Nature - the trees, the grasses, the animals of the place, everything about it delighted him.

"It was like 100 B-12 shots for him just to see the trees and Nature."

So she was much moved, she said, visiting the LBJ Grove, the memorial covering 12 acres of Lady Bird Johnson Park on the island across from the Pentagon. She sat there and did a little communing with Nature herself and concluded the late president would have been well pleased by this memorial.

Rosalynn Carter presented awards for landscaping excellence nationwide, at ceremonies in the East Garden now fresh with rosemary, heliotrope, clipped hollies and the lime trees in flower. She handed out 45 plaques to winners in the competition staged by the American Association of Nurserymen, and some of the winners had assistants and colleagues with them, so that one way and another Mrs. Carter shook 300 hands and looked straight, smiling and sincere, into 600 eyes.

President Carter has planted a red maple (Acer rubrum) on the grounds, and Mrs. Carter has planted a red Japanese maple (Acer palmatum 'Bloodgood') and seemed pleased to take her place in the long line of tree planters.

"That's the magnolia Andrew Jackson planted," she said, nodding toward it, now in bloom and looking as goog as the great magnolias of Tennessee where it came from.

"Now you all come inside for some refreshments, just follow me," she said, and everybody did so, forming a line to shake her hand a second time, before wandering through the state rooms drinking iced tea and taking care not to slop the stuffings of small eclairs on the rugs.

There were brief speeches, all to the general effect that corporations and governments are planting trees and flowers, at long last.

Marc Cathey, who has been president of the American Horticultural Society and is an important researcher in the Department of Agriculture at Beltsville, was being greeted as Super Thumb, and epithet he is not totally pleased to become known by.

The Laurance Rockefellers, who helped raise private money for the LBJ Memorial Grove, were among the guests, along with the grove's landscape architect, Meade Palmer of Warrenton.

Preeminence in landscaping of their corporate offices at St. Louis brought an award to McDonnell Douglas, whose three-wing building has been embowered with trees. Other major winners included the San Diego Wild Animal Park and Valencia Community College in Florida.

Richard Castleberry of suburban Denver said it snowed at home last night, as he crossed Pennsylvania Avenue snow-free with his large plaque and Japanese maple tree, souvenirs given by the White House.

"Wouldn't want to live here," he said, heading for a bar and a cold beer.