President and Mrs. Carter had the entire Congress, two diplomatic corps (those accredited to Washington, and those accredited to the Organization of American States) and the military establishment in for cookies on Saturday.

It made a long day, but there are not many people left in town whom the Carters owe.

Altogether, it was about 2,400 hands that the Carters shook. They did not go in for wholesale kissing of generals and ambassadors the way they had on Friday, when it was hometown folks and grass roots supporters they were entertaining.

The parties looked increasingly formal as the day wore on, not so much because of the hours, but because of the type of guests.

Members of Congress, in the morning, were the least formal, with some of the men in plaid pants, and a lot of women in pants. The diplomatic corps exhibited lots of three-piece suits and ultrasuede dresses, plus a few native costume numbers, including the Chilean ambassador to the Organization of American States in Spanish riding clothes.

The military, in the late afternoon, was exhibiting gold braid, of course. Among their wives there were some long dresses, patriotic jewelry - a five-star diamond pin on Mrs. Omar Bradley, sparkly flags on the lower ranking - and mink stoles. The last was a practical addition, since President Carter had ordered the White House thermostat turned down to 65 degrees earlier in the day.

The President wore his version of formal clothes throughout the day - a blue suit with brown shoes. Mrs. Carter wore a long-sleeved white dress with buttons down the front in the morning and a ditto in blue for the afternoon.

Chief of Protocol Shirley Temple Black presided at the diplomatic reception, and said it was her last official function. Her replacement will be announced early next week, she said. While she claimed not to know who it might be, she said she thought it was a man and that his initials were not S.B. (for Smith Bagley, the wealthy Carter campaign supporter).

Each of the diplomats had his photograph taken with Mrs. Carter holding onto his arm, while the President held Mrs. Carter by the hand or around the waist. Members of Congress were processed through more quickly, with a half-hour or more wait in line, a handshake and then out the door.

At each reception, Vice President and Mrs. Mondale ran an auxiliary receiving line several yards away.

The Juilliard Quartet played with the diplomatic reception, the Kalichstein, Laredo and Robinson trio for the armed forces and "Music From Marlboro" for Congress.

With the assembly-line technique, significant happenings were scarce, unless you consider that President Carter kissed the wife of the Israeli ambassador, and the ambassador of Guatemala clicked his heels smartly, first to the President and then to Mrs. Carter.

Sen. Edmund Muskie announced that the country was reacting positively to the Carter administration - a fact he had gathered from his sister in Rumford, Maine, who was in a position to know how the people felt because she talked to a number of them at her retirement party from a paper mill.

And diplomats, as always, picked up useful information. The ambassador from Somalia found himself standing in front of the President, who took the opportunity to tell him, "Hi, my name's Jimmy Carter."