The end of the old year brings a painful duty: the annual exercise in self-humiliation known as mea culpa time. It involves re-reading the columns that came out of this typewriter in the past 52 weeks and asking, "How could I have been so dumb?"

The easiest ones to deal with are the straight-out goofs. Take, for example, the following letter from Rep. Lee H. Hamilton (D-Ind.):

"In the lead sentence of one of your recent articles from Louisville you suggested that the Louisville Slugger (baseball bat) is made in Louisville. I simply could not let such a grievous (but understandable) mistake go uncorrected. Since 1974 they have been made in Jeffersonville, Ind."

Jeffersonville, as you might have guessed, is in Lee Hamilton's district. I now know that, as well as its most famous (if borrowed) local product. Live and learn.

Another letter is from the economist Walter W. Heller, to whom I had attributed the thought that the wave of mergers among giant firms was like "dinosaurs mating." "Nice phrase," Heller said, "but not one I ever uttered."

Recourse to the notebook produced the discovery that the name squiggled in front of that line was Mueller, not Heller, thereby proving, 40 years too late, my fifth-grade teacher, Miss Schilling, was right when she said that no one with my messy handwriting was ever going to succeed.

A third goof was a total mental lapse. On May 17, in a column about President Reagan's budget victory in the House, I wrote that after they had lost the key vote substituting the Reagan-endorsed Gramm-Latta budget for the committee bill, "more Democrats, including Rep. Jim Jones of Oklahoma, the architect of the Democratic counter-budget, slipped over to vote with Reagan on final passage."

The hint of surreptitious weasling on Jones' part was totally unjustified. The rules of the House require that the majority of conferees have supported the position of the House on a bill. If Jones as chairman of the Budget Committee wanted to head the House conferees in their dealings with the Senate, it behooved him to vote for the amended budget.

Those were the three big goofs in my file. And if you think it was coincidence that they all involved Democrats, you underestimate the journalistic reflex to "kick 'em when they're down." There were a number of columns where the kicks I aimed at the Democrats for their stumbling performance were deliberate, although, as the year progressed, there were more frequent hints that the opposition party was beginning to get its act together.

What really stands out in re-reading the file is the ambivalence on Reagan and his works. Throughout the year, I seemed unable to make up my mind whether he had been cast as Paul Bunyan, felling the giant oaks of liberalism, or as Humpty Dumpty, riding for a fall. On alternate weeks, and sometimes on alternate days in the same week, you could read both views in this space.

His politics were described as masterful, his economics as implausible. His ability to bend Congress to his will was noted with wonderment. But there was astonishment at the sweeping misinformation he disseminated and the startling ignorance he displayed in some of his press conference comments.

As the year ends, I am still uncertain about how long fancy political footwork can make up for the substantive gaps and the policy weaknesses in the president and his administration.

As for the president's men, I don't think I was wrong in suggesting that Ed Meese was going to be tough on civil liberties, or that the Justice Department was foot-dragging on voting rights and civil rights, or that Dave Stockman's intellectual shiftiness was creating credibility problems for the administration on Capitol Hill even before the Atlantic Monthly interview.

I was certainly not wrong in saying that Max Friedersdorf was one of the ablest congressional liaison men any president ever had. But I was wrong when I blamed Wall Street for non- support of the newly enacted Reagan economic program. The problem, I now see, was not on Wall Street but on Main Street: the recession was coming.

The piece whose thesis is least likely to be proved wrong in the long run was the first of the year, talking about the start of a new decade and a new administration.

"The mood," it was said, "is hardly buoyant, but it is realistic--and there is a lot to be said for that. It is plainly going to be a time of hard choices, but that knowledge creates a climate where sensible debate may proceed without the disabilities of a dream world where all good things may be done at once."

If I had been smart, I would have quit with that paragraph--the second paragraph of the first piece of the year. But instead, it was on through the vagaries of Jeffersonville Sluggers and Mueller's dinosaurs and now into 1982. Caveat lector--let the reader beware.