Before Jimmy Carter was elected President, he smiled so much we wondered why. Now he seldom smiles, but at least we know why . . . This is the last column I will be able to write for at least a while, and there is much I'd like to include in it, so please forgive its abbreviated reports . . . Several District Liners were irate when they received chain letters that had apparently been photostated on government copying machines and then mailed in franked envelopes that bore the return address of the Deputy Secretary of Transportation. Alan Butchman, the deputy sec, has turned te case over to Dot's investigative force . . . Tom Garasic notes that the owner of Loeb's Restaurant on 15th Street NW has a wry sense of humor. A sign in Loeb's window says, "We are now making a little effort to be pleasant for a limited time only.As soon as business picks up a bit, this will stop" . . . When Bob Orben heard that it will cost $6 a barrel to bring Alaskan oil to the West Coast, he mussed, "They must be bringing it 800 miles by pipeline and the rest of the way by cab."

TWO WEEKS ago, I advised the finder of a pair of eyeglasses that I cannot publish lost-and-found items because hundreds of things are lost and found in a big city every day. Since that item appeared, 31 people have called or written to say. "I'm sure those were my eyeglasses you wrote about" . . . As usual, my defense of the Postal Service has brought in several letters of Bowl America, tells me that payroll records from BA centers in Jacksonville and paychecks from Washington to Jacksonville must now go by Special Delivery because ordinary mail between the two cities seems to move by way of Outer Mongolia . . . One local agency is unique with regard to complaints. I receive frequent calls and letters from District Liners who have used the services of the Automobile Owners Action Council (1411 K St. NW. 638-5559) but I have never gotten a single complaint about that group. Amazing! . . . When the lights went out in New York, Mayor Abe Beame's first thought must have been, "Did we default on the light bill?" . . . At least 40 per cent of reader response to my suggestion that makes should shed their jackets and ties during hot weather has been from men who are opposed to the idea. Richard A. Pence of Fairfax, who was among the majority, suggests that during hot weather the picture that accompanies this column should show me in an open shirt, sans tie. That's a good idea, and next year I promise to do it, especially if there is a next year.

ONE WHO presents himself to the public in the hope of winning its approval must expect some loss of privacy, whether he be a politician, entertainer, athlete, or even newspaper reporter. Those who buy the product have a right to be curious about the person who produces it.

Accepting this thesis, I recently provided readers with a report on my heart catheterization. I now offer an update on more recent developments.

The catheterization indicated I need a new heart valve and a coronary bypass, and I will therefore undergo sugery next month. If all goes well, I will be permitted to return to Washington two weeks after the operation, and thereafter to engage on limited but gradually increasing activity. The surgeon says my chance for a good outcome is 95 per cent, but I must make no commitment to go back to writing on deadline for three months.

There is little that a man can say when he doesn't know whether he is destined to be part of the 95 per cent group of part of the 5 per cent group. But if this is to be my last column, there is no better way to end it than to tell you that I am grateful for your help and your patience, and to ask you to keep a light in the window for me.

We shared a few laughs and we hit a few licks for good causes - and that, I think, is what life is all about. I'm content.