Everybody was trying to take credit - Texans, Californians, Floridians.

"A Georgia-type night," corrected a Georgian who, as it turned out, had the last say.

He was Jimmy Carter, welcoming an estimated 1,000 members of Congress and their families to a White House picnic and concert Saturday night on the South Lawn. Overhead, a nearly full moon hung suspended like a stage prop.

In a skyrocketing grand finale that rivaled the pyrotechnics of a Fourth-of-July celebration (some even thought of the Bicentinnial's), conductor Andre Kostelanetz led musicians in a Washington, D. C., adaptation of his now-popular New York City "Promenades" concert.

This one combined 120 red, white and blue uniformed musicians from three military service symphony orchestras for a rendition of Tchaikovsky's "1812 Overture." Children screamed and parents gasped. Outside the White House, tourists came to a neck-craning stop. The brilliant colored rockets and starbursts all but eclipsed the pale yellow moon.

Carter had warned his guests to expect something out of the ordinary.

"I think when you hear the last selection," he said, "it will remind you of the kind of leadership breakfast I have with the congressional leadership every two weeks."

For this evening, however, fireworks were confined to the heavens. What seemed to impress Carter almost as much as Kostelanetz's 52 million record sales was his ability in "getting perfect harmony from three different military services - which is something I have not always been able to achieve myself."

Before the concert the evening was punctuated with handshaking, picture posing and a bit of kissing. During the concert the president took off his reptie, then his blue blazer, and pulled onto his lap a couple of youngsters seated nearby. Army Carter was conducting whirlwind guided tours of the White House and her tree house, located behing the stage, for any junior guest following in her trail.

Neither the president nor Mrs. Carter joined their guests in eating the pate du chef de maison, smoked salmon from Washington state, miniature chicken legs and Port Salut cheese, all packed into special boxes on tables festooned with pots or geraniums.

"We eat upstairs," Carter told a reporter. "It's more important to shake hands."

He shook a fair number, and in the process paused to talk briefly with Stens. John Sparkman (D-Ala.), Wendell Anderson (D-Minn.) and Dale Bumpers (D-Ark.) On the House side, there were quick words with Reps. Hames Howard (D-N. J.), Gus Yatron (D-Pa.), Leo Rvan (D-Calif.) and George Manon (D-Tex.), as he passed among picnic tables borrowed from the National Park Service.

Carter spotted Rep. Jack Brooks (D-Tex.) packing away four napkins and a matching tablecloth created especially for the picnic by a New York designer Calvin Klein. Carter asked with a grin, "Who's that stealing my tablecloth?" Brooks also grinned - and blushed.

No felony committed or intended, however. The cloths were meant to be taken home as mementos of the evening, Carter announced.But some in the crowd didn-t stop with just one.

They were what Mrs. Fred Rooney, wife of the congressman from Pennsylvania, called "card-table size." So the Rooneys, who shared a picnic table with Rep. and Mrs. Thomas L. Ashley (D-Ohio), took home two table-cloths and four napkins while, she said, the Ashleys took home the two tablecloths covering a neighboring table where the Ashley and Rooney children sat.

"I mean we were told to take the tablecloths," said Mrs. Rooney later, adding that "it was a funny feeling to be at the White house and going home with the tablecloths."

The whole idea of the evening had been to make it an all-family event for men who lead the country and "who represent not only the political structure of our government, but also try to exemplify for political and other reasons fine, solid and exemplary inner family relationships," said the president.

He admitted he had an advantage over his guests who do not have "an easy time" being close to their families.

"For Rosalynn and for Amy and for me this is a wonderful occasion - we have the advantage as a family along with Chip and Caron, Jeff and Annette, and James, to live very close to where I work." He outstayed most of his guests, who had gone home with the napkins and tablecloths and, in several cases, the pots of geraniums as well.