Outside Ron Nessen's windows, a small, puffed-up mockingbird hops around on a heating grate, trying to get warm. Inside Ron Nessen's office, devoid of books, devoid of pictures, devoid of almost everything except Ron Nessen, things look equally bleak.

"It's like a divorce. That's the only thing comparable," Nessen says, looking around at a couple of plants, an odd candlestick, a shopping bag, a broken shelf, the flotsam of a political exit. "Saturday was sad. Everybody packed up, took their pictures home. I've been taking a shelf of books home a night."

It is the end of day for the Ford White House. "Why isn't anybody paying any attention to me, it's all slipping away," Nessen said in mock horror before his Tuesday press briefing and later, more seriously, he said "the feeling, and I've even heard the President talk about this, is the most of the work is done. These last few days people are getting a little bit itchy to move on to the next thing."

Transition now takes on a distinctly physical meaning. Ford people, objects and animals - Susan's cat, Shan, the dog, Liberty - move out. Carter people, objects and animals - cats Misty Malarkey Ying and Sawshoes, dogs Grits and J.B. - move in.

Jack Ford, wandering around the press room, said he really moved two weeks ago, he's only back to do a TV bit with Barbara Walters. Most of the Ford furniture is already packed up in a warehouse, ready to be trucked out to California. The bed will go out this morning, to be replaced by an 18th-century Philadelphia Chippendale, a four-poster that was last used by Mrs. Nixon.

At the stroke of noon, the Carter folks march in, like Sherman through you-know-where. Ann Anderson, Mrs. Carter's deputy press secretary, and Mrs. Carter's staff hope to be "the irstest with the modest," and Ann Ander herself will march in with her large Dracena Marginata plant in hand.

Somehow, in between the marching in and the marching out, funny things take place. All those glowing pictures of President Ford with his hands outstretched in victory, photos that even now look suddenly faded, will disappear and Carter photographs emerge in their place.

"It's little elves around here, I guess," Nessen says, though it does appear that staff members who want a particular picture can put their names on the back and just take them when they go. One secretary mentioned a portrait of Mrs. Ford and Paul Newman and promised stoutly, "they won't take that away from me."

Much of the White House has taken pains to look like nothing has changed. When President Ford removes a shelf of his books, government-owned books are rushed in to fill the unsightly breech. In the Cabinet room, new unmarked chairs have discreetly replaced the name-tagged ones that Vice President Rockefeller and Henry Kissinger have purchased. Today, Ford's staff will present him with his chair, purchased from GSA or 63 $10 checks, a sizable incease over the $400 President Johnson's chair cost way back when.

Ironies clutter the final days. The same wholesome, All-American menu that the Fords and the Rockfellers ate last night - roast beef, baked potatoe, popovers, fresh green beans, tossed green salad and vanilla ice cream - will be eaten by the Carters tonight. Some things never change.

And then there is Ron Nessen's goodbye gift to Jody Powell, who inherits his office as well as his job. "About a year and a half ago, when briefings were fairly heated, some friends from the Justice Department sent this over," Nessene explains, moving to a closet in the corner of his room. Inside is a nifty, blue brocade vest, to which the following note is attached:

"Dear Jody,

"This is a bulletproof vest. I hope you won't need it.

"Good luck,

"Ron."