As far as free goods go, ace pitcher Rich Harden is unsurpassed. Having pitched just 200.1 innings from 2005 through 2007, the 26-year-old is no staff anchor, but when fit to take the mound, he’s spectacular, as evidenced by his line this year — 77 innings, 92 strikeouts, 31 walks, five home runs, and a tidy 2.34 earned run average. To get him at all would have been a coup for Jim Hendry, who runs the Chicago Cubs, the best team in the National League. To get him for nothing, as he did Tuesday, was something else. The City That Works owes this man many beers.

The key to the deal wasn’t Harden, but Chad Gaudin, another pitcher who made his way from the Bay Area to the shores of Lake Michigan. A 25-year-old swingman who was solidly average in the Oakland rotation last year, he’s every bit as good as Sean Gallagher, the 22-year-old starter who was the best player the Cubs gave up in the trade. (The main differences are age service time — Gaudin is eligible for arbitration, while Gallagher won’t be for years.) In essence, Chicago swapped two fourth outfielders for whom they had no use and an A-ball catcher who will probably never make the majors to fill the Mark Prior memorial slot in their rotation, a slot reserved for dominant pitchers who can’t be counted on for anything past their next pitch. That’s a great deal.

While widely cast as a quick response to Milwaukee’s Monday trade for Carsten Charles Sabathia, Chicago’s deal really was nothing of the sort. Third in the league in ERA, and first in rotation ERA, the Cubs didn’t need actively need help, as Milwaukee did; nabbing Harden at this price was more the equivalent of bending over to pick up a $20 bill on the street. The Central Division won’t turn on these moves, but on the rather glaring weaknesses of the contenders, which are a lot more significant than even the most glamorous trades.

For the Cubs, the problem is located everywhere that isn’t Wrigley Field. Four key Cubs — Aramis Ramirez, Alfonso Soriano, Kosuke Fukudome, and Mark DeRosa — have home batting averages more than 100 points higher than their road marks. The first three are outright pitiful on the road — Ramirez’s road on base average is .282, Soriano’s is .280, and Fukudome’s is .312, which is actually higher than his slugging average. Maybe the Cubs have taken advantage of some odd Chicago weather; maybe they’ve benefited more than usually from their traditional creative groundskeeping; maybe they’ve been lucky; maybe there are eyes, or binoculars, in the ivy. Whatever the case, their league-best scoring has been entirely driven by home cooking, as they’ve collectively hit an absurd .311 BA/.391 OBA/.502 SLG at home, as opposed to .257/.331/395 abroad. (Their pitchers have been better at home than on the road, but not unusually so.)

It shouldn’t be controversial to say that the Cubs can’t possibly hit this well at home for the rest of the season. This leaves an opening for Milwaukee and St. Louis, both within striking distance of the division lead. As it turns, though, they have their own, equally substantial problems.

St. Louis’s issues are self-evident. Their offense basically consists of Albert Pujols, Ryan Ludwick, and Rick Ankiel. Pujols is the best hitter in baseball; Ludwick is a career fifth outfielder, and Ankiel is a converted pitcher. The latter two are terrific stories, but it’s unlikely that they’ll to continue to hit like Vladimir Guerrero. It’s equally unlikely that career relievers Braden Looper and Todd Wellemeyer, and career no. 5 starters Joel Pineiro and Kyle Lohse, will all continue to pitch like durable no. 2 starters. If it does, hats off to manager Tony LaRussa and pitching coach Dave Duncan. They’ve turned dross to gold before. More likely, St. Louis is going to start feeling the effects of gravity sometime very soon.

Milwaukee’s issues are less glaring, but equally real. They do have some things going for them — infielders Bill Hall and Rickie Weeks are good bets to pick up their play in the second half, and although center fielder Mike Cameron has been very good, he’s also batting .227. Any improvement over that low bar would really help. Still, their staff has been quite dependent on the health of injury-prone ace Ben Sheets and on top-rate performances from elderly relievers Salomon Torres and Brian Shouse, both of whom are very good despite their obscurity but neither of whom are the sort you really want to build your bullpen around. Sabathia will be a tremendous help, but for every bit of improvement they can expect in the second half, there’s an equal bit of decline they can expect, and to date the team is, like St. Louis, outperforming its run differential, often a sign of looming trouble.

Altogether, the Harden trade is more likely to have an impact on the playoffs than on the regular season. The Cubs have real issues, but they’re also just better than these other teams, especially the Cardinals, and they’ll be so even if Harden makes his expected trip to the disabled list sometime soon. Whether Duncan’s fairy dust continues working and whether Hall and Weeks ever come around will probably count for more in the end than the state of Harden’s fragile, electric right arm.

tmarchman@nysun.com