While the rest of the world has been performing feats of strength, listening to Brenda Lee, pretending they like roasted nuts, and enjoying other seasonal traditions, it seems the Yankees have been busy talking about trading Randy Johnson, who has let on to team management that he wouldn’t be devastated if the club managed to move him closer to his Arizona home.

Most Yankee fans would likely consider it a fine holiday gift if general manager Brian Cashman were able to ship the freakish legend out of town. It’s one thing to have a 43-year-old pitcher with a bad back and bad knees coming off a year in which he posted an ERA of 5.00 on your team. It’s still another when that pitcher is known about town as much for gas-facing an innocent cameraman and ending up on the front cover of the Post for his supposedly shabby treatment of an illegitimate child, as for his crummy pitching and irritating demeanor. Still, bum though the Big Unit may be, the Yankees ought to be cautious about trading him. As much as the team would lose in obscene nicknames and monstrous unattractiveness, they would probably lose more in the standings.

The unpleasant fact about Johnson is he may well be the Yankees’ best starting pitcher. Take that 5.00 ERA, for instance. It was bad, but Johnson’s underlying performance was good. His component ERA — a number derived from the hits, strikeouts, and so on, he allowed — was 3.81 in 2006, 13th-best in the American League. In fact, the disparity between the two numbers was the highest in the league. Component ERA, for a variety of reasons, is a better predictor of future success than actual ERA, and statistically, Johnson looks like an excellent bet to post an ERA of around 3.75 this coming season — a better bet, actually, than any other Yankee starter.

He may also be a pretty bad bet to do so. The big gap between the two ERA figures is the result of the fact that Johnson couldn’t get anyone out once runners reached base. He allowed a .564 slugging percentage once men reached against him — the worst among qualifying starters in the league. This would support the subjective impression anyone who saw the man pitch in pinstripes this year would get: Johnson would pitch well for a few innings and then fall apart before being utterly hammered and marching off the mound in disgrace with slumped shoulders and a bewildered expression on his pockmarked mug.

The basic question facing the Yankees is whether this is likely to be repeated. It’s worth keeping in mind that Johnson was pitching with an injured disc in his back, which had a lot to do with the relatively flat slider he was throwing from the stretch. That disc has been repaired by surgery, so any mechanical problems that were leading to bad pitching in the clutch should, in theory, be more easily corrected now that the big man is in better shape. And if it’s corrected, and he pitches otherwise as well as he did the last two years, he should rank among the dozen or so best starters in the league, no longer the fearsome animal who dominated the National League for years while in his prime, but a valuable pitcher all the same.

Still further complicating things is that he’s really old. Johnson could solve all his mechanical problems, bestride the mound in perfect confidence, and still see the effects of age cancel out any gains gotten by surgery and rehabilitation.

Basically, every factor that works in Johnson’s favor is canceled out by another working against him. No one can say, whatever his component ERA is, that he looked much like a 3.75 ERA pitcher this past season. Nor does he seem likely to be one any time soon. On the other hand, he’s done all sorts of unlikely things in his career and, as Roger Clemens has shown, the combination of a pitcher who ranks among the best in modern history can — with medical advances — produce remarkable things. I’d take the over on that 3.75, but not with any real degree of confidence.

Cashman ought not trade Johnson unless (a big unless) he gets some good, young talent in return. If he can extract that from the Diamondbacks, who have a loaded farm system, he should by all means take it. The Yankees, given their fairly strong rotation, only need Johnson to throw 150 innings of 5.00 ERA, and they should be able to replace that if they deal him. They would, though, be dealing in Johnson, a pitcher with the best chance of being a full-blown ace and thus, of being able to sustain the rotation through unforeseen difficulties.

They can afford to trade him easily enough, but they really have no need to do so. He’s not only nowhere near so bad as is generally thought, he’s actually, on the whole, a valuable asset, especially as he’s only signed for one year and $16 million, which isn’t a frightening commitment these days.

All of this only takes in the baseball side of the picture, of course, and I can’t argue with anyone who wants Johnson gone strictly on aesthetic grounds. Still, if expectations are raised by reports of trade talks, no Yankee fan should feel a bit of disappointment if the five-time Cy Young Award winner returns to the Bronx. It might actually be for the best.

tmarchman@nysun.com