Nets fans, the time for drastic action is nearing.The team has undergone an abrupt personality change in recent months, and the only way to bring back the old Nets might be to trade one of their best players.

Let’s start from the top. A year ago, the Nets were a good defensive team hamstrung by its complete inability to score. Now, they have the opposite problem. New Jersey’s offense is clearly of a playoff caliber, even with Vince Carter not quite firing on all cylinders yet. But the defense is nowhere to be found.

Now that we’re a month into the season, it’s officially Time To Start Getting Worried. Tuesday’s loss to the Pistons dropped the Nets to 7-8, making preseason predictions of an easy romp to the Atlantic Division crown look silly. The Nets wouldn’t make the playoffs if the season ended today, and they’re looking up in the standings at a mediocre Philadelphia team that gave them Marc Jackson virtually for free before the season.

The Nets are 7-8 because the defense – the team’s one consistent strength throughout the Jason Kidd era – has suddenly failed. Defensive Efficiency, my rating of how many points a team allows per 100 possessions, tells a depressing story. Last season, New Jersey gave up 100.4 points per 100 possessions, the seventh best rate in the league. This season, that number is up to 103.2, even though scoring around the league is 2.1 points per 100 possessions lower.Thus, relative to the league, the Nets are allowing nearly five points per 100 possessions more than a year ago, and their ranking has dropped from seventh out of 30 teams to 25th.

That drop in defensive effectiveness has more than offset the much expected improvement in New Jersey’s offensive numbers. With Richard Jefferson healthy, Nenad Krstic improving, and Carter in town for a full season, the Nets rank 11th in Offensive Efficiency (the counterpart to Defensive Efficiency). Last season, they finished 27th.

Unfortunately,the way the Nets have done this is by pairing Jefferson and Carter on the wings. This is a great offensive setup, but defensively it requires one of them to be the stopper on the wings. Neither seems up to it. Carter has been a sluggish defender his entire career, so it was unrealistic to expect him to step up. That made Jefferson the stopper by default, but he has disappointed in that role. As a result, opposing wingmen are having a field day against New Jersey.

Take the Pistons game. The Nets allowed their opponents repeated open looks from the 3-point line – Detroit finished 10-for-20 – and forced only 10 turnovers. Despite playing on their home court, the Nets allowed 93 points on 86 Detroit possessions, a ratio that nearly always produces a loss.

As they have all season, the Nets struggled mightily against a top-flight shooting guard. Richard Hamilton made 10 of 14 shots from the field and burned the Nets for 30 points, again exposing Jefferson’s inability to contain quick guards. Three nights earlier, Kobe Bryant went off for 38 points in the second half and nearly fouled-out half the Nets’ roster in the process. It wasn’t even the first time an opposing shooting guard hung 30 on the Nets in a half – Tracy McGrady did it two weeks earlier.

The problem isn’t with Jefferson per se, but rather what he’s being asked to do. As a 6-foot-7-inch small forward, he’s not nimble enough to stop smaller players from beating him around screens or taking him off the dribble, especially when the Nets lack a shot-blocker inside to back him up. When those players get a step off the dribble, it forces the Nets to help from the weak side and leave openings for perimeter players away from the ball.

That 3-point shooting performance by Detroit on Tuesday was no accident – the Nets have been killed by the long ball all year. Through Tuesday’s games, New Jersey had allowed a whopping 116 3-pointers on the year – 20 more than any other team. In fact, if the Nets just allowed an average number of 3-pointers and replaced the rest with 2-point baskets, they’d be near the league average in total Defensive Efficiency.

All those open jump shots are having another effect – the Nets can’t force any turnovers, because opponents rarely have to handle the ball in traffic. New Jersey’s opponents have made miscues on only 13.9% of their possessions, ranking them 26th among the 30 teams. Again, if the Nets were merely average in this category,it would slash nearly two points off their Defensive Efficiency rating and pull them within hailing distance of the league average in points allowed per possessions.

Knowing the weakness is there doesn’t help solve it, of course; the dilemma for coach Lawrence Frank is what to do about it. It’s not like he can bench Jefferson. He has few players in reserve that are palatable options to use as a wing stopper – so much so that Jacque Vaughn, though utterly bereft of offensive skill, has made frequent cameos of late.

That’s why, if the Nets’ defensive malaise continues, more radical surgery may be in order. If the Carter-Jefferson pairing on the wings can’t work, perhaps it’s time to see what Jefferson can bring in a trade. Suppose the Nets found a trading partner willing to give them a good, young defensive stopper with a jump shot and a decent frontcourt player in return for RJ. Could the Nets really pass this up? Before you start laughing, consider that Dallas (Josh Howard and Keith Van Horn), Golden State (Mickael Pietrus and Troy Murphy), and New Orleans (Desmond Mason and P.J. Brown) all have combinations of players and salaries that are workable.

Thus, the next few weeks are important ones for the Nets and for Jefferson. The only way the Carter-Jefferson lineup on the wings can work is if Jefferson can stay in front of opposing shooting guards. Otherwise, it won’t matter how good the Nets’ offense is, because they won’t be able to offset the deluge of 3-pointers raining down on them every night. If the next 15 games go like the first 15 did, it could portend an outcome unthinkable a few short weeks ago: RJ in a new uniform by the trade deadline. It may be the only alternative to a hugely disappointing season.

Mr. Hollinger is the author of the “2005-06 Pro Basketball Prospectus.” He can be reached at jhollinger@nysun.com.