With their 106-105 loss on Tuesday night to the Miami Heat, the New Jersey Nets began what will no doubt be a sour off-season for both team officials and fans. After surprising the Heat with an efficient Game 1 victory in Miami, the Nets dropped their next four, the last three of which were winnable games that were lost in large part by failing to execute down the stretch.

Given that a different bounce of the ball here or there in each of those last three games might have left this space devoted to a discussion of the Nets’ chances in the conference finals, it’s tempting to declare the season a success and recommend only a few summer tweaks for team president Rod Thorn. However, the Nets on paper lacked a lot, and Thorn and his braintrust, particularly head coach Lawrence Frank, have a lot of work on their hands if they are to reach – or even come close to – the conference finals in 2007.

First and foremost, it’s time to overhaul the status quo and blow it up. Not the roster, or at least the nucleus – guards Jason Kidd and Vince Carter and forwards Nenad Krstic and Richard Jefferson comprise one of the strongest starting quartets in the NBA – but the philosophy. The problem is in the blueprint of the team’s offense.

The Nets are generally regarded as an uptempo team, led by a quick-thinking point guard (Kidd) who loves to run the break and two magnificent dunkers (Carter and Jefferson). But the reality is that the Nets haven’t played faster than the league average since 2003. The 2003-04 team finished 18th in Pace Factor (possessions per contest), the 2004-05 squad finished 21st, and this year’s crew returned 18th. It’s a much more deliberate offense than is commonly assumed.

There’s nothing especially wrong with playing at a slow tempo if the offense clicks. Dallas (27th in Pace Factor) and Detroit (29th) played some of the slowest ball in the league this season, but it didn’t stop them from finishing with two of the NBA’s three best Offensive Efficiency ratings, which measures points per 100 possessions. The Nets however, lumbered their way to 24th in Offensive Efficiency. That was an improvement over the 2004-05 bunch, which finished 27th, and the 2003-04 unit, which ranked 25th.

The Nets’ slower tempo would be understandable if the team had a big man, like Yao Ming, who needed a slower pace to come down and set up in the halfcourt offense. But Nets pivotman Jason Collins doesn’t fit that mold. In fact, all five Nets starters run the floor well, and Kidd is a master orchestrater of the fast break. Thus, before roster upgrades are even considered, the first thing the Nets need to do is change the game plan to turn up the tempo. It’s a better fit for their talent and it should help what is often a moribund offense.

The second thing the Nets need to accomplish in the off-sesaon is to import a better supporting cast. Of course, the Nets have needed a better supporting cast since their first trip to the Finals in 2002, but the situation is growing more urgent. At present, the Nets are the third-best team in the NBA’s second best conference, and there are several teams – notably Cleveland and Chicago – coming up fast on them. Without bolstering their depth, the Nets could easily find next year’s postseason run ending two weeks sooner.

The Nets will first need to spend time maximizing last year’s draft picks, Antoine Wright and Mile Ilic. Wright, a 6-foot-7-inch swingman out of Texas A&M, was taken with the 15th pick, and his rookie season was a nightmare. To say he looked overmatched in the pro game is putting it lightly; Wright shot 35.8% from the field 6.7% from behind the arc (yes, 1-of-16), and he even clanked half of his free throws. Sadly, his best asset was supposed to be his stroke. The Nets will need him to find it this summer or he’s a bust.

Ilic, a Serbian pivotman listed at 7-foot-1,spent the year in Europe and may come over for next season. If he has learned to bang in the Euroleagues, it would address one of the team’s biggest weaknesses: offensive rebounding. The Nets finished 29th in the league, boarding only 24% of their own missed shots. Just as pushing the tempo would create more possessions for Carter, Jefferson, and company, so too would doing a better job of cleaning the glass.

The Nets have two first-round draft picks – their own at no. 23 and the Clippers’ at no. 22. They would do well to use them to bring in more size. It’s hard to gauge who will be left at that stage of the first round, but many mock draft boards have the Nets taking 20-year-old Senegalese center Saer Sene, an athletic pivotman who blocked one shot every 10 minutes and averaged 12 minutes of play and 16 boards per 40 minutes in the Euroleagues.

Sene could be the next coming of the Orlando Magic edition of Darko Milicic, a shot blocker who boards well. Sene’s offensive game isn’t well developed, but that isn’t a need in a lineup featuring four scorers. Besides a new rebounder, the Nets need a shot blocker; the team ranked 25th in free throws allowed per 100 shots this season, a sure sign that opponents are getting to the rim without a second line deterrent in the otherwise stout Net defense.

The Nets will also have their midlevel exception, which won’t be enough to attract top free agents like Indiana’s Peja Stojakovic or Atlanta’s Al Harrington, but the team should be aggressive in seeking swingmen who can shoot.

Most important, the Nets need to tackle this off-season with a win-now mindset. The window of championship contention for the Kidd-Carter-Jefferson-Krstic Nets is closing quickly. Kidd is 33, and his skill set is beginning to erode. Carter, still among the most explosive players in basketball, can opt out of his deal after next season. The Nets have had a stellar run as an elite team, but next season might be their last go round before they have to start making major personnel changes.

mjohnson@nysun.com