Judging from their personnel maneuvers early in this off-season,two of the NBA’s best teams, the San Antonio Spus and the Dallas Mavericks, are stuck in the past. Their transactions suggest they’re still trying to reverse their final losses of the 2005–06 season, rather than looking to compete next season.

The development is somewhat surprising because both teams are generally model franchises, especially well-regarded for their work in talent development and shrewd personnel judgments. Yet the Spurs have jettisoned both of their centers, leaving the team perilously thin in the paint (yes, there’s Tim Duncan, but little else). The Mavs, meanwhile, have weakened themselves on the wings.

The Spurs’ strategy to look for smaller, quicker players was understandable after their loss to the Mavericks in the Western Conference semifinals. Dallas utilized a small lineup, often using Keith Van Horn — a small forward in most lineups — as a center, and ultra-quick guard Devin Harris to push the tempo. The Spurs — a classic, big center, lowpost power forward-style team — struggled to keep up. Their pivotmen, Rasho Nesterovic and Nazr Mohammed, could barely get off the pine because there was no opponent they could guard effectively. Dallas’s speed had turned one of San Antonio’s assets — strong play in the pivot — into a weakness.

So far in the off-season, the Spurs have traded Nesterovic to the Toronto Raptors in exchange for Matt Bonner and Eric Williams, two forwards who mostly live on the perimeter. Then they watched as Mohammed, a free agent, signed with Detroit. Suddenly, the Spurs’ depth in the pivot had vanished. Fabricio Oberto, a 31-year-old rookie from Argentina who saw only 492 minutes of (mostly garbage time) burn, is the now lone option at center. Putting Duncan at center leaves Oberto and the aging Robert Horry as the only options at power forward.

The Spurs are said to be interested in Nuggets center Francisco Elson, but by clearing out the incumbents, they have put themselves in a terrible bargaining position. Also, since when did Elson become anyone’s idea of a solution? In three seasons with Denver, the 29-year-old from the Netherlands has done little to look like a starting NBA pivotman. Even last season, when the Nuggets were desperate for anyone to play the five, Elson managed just 4.9 points and 4.7 boards in 22 minutes per game.

If the Spurs don’t shore up their pivot situation, it will mark their second straight bad off-season. Last summer, they eagerly signed up Oberto, swingman Michael Finley, and guard Nick Van Exel. Of that trio, only Finley paid any dividends,and he’s 32 and clearly declining.The Spurs’ front office has had a long run of stellar successes, including drafting all-stars Manu Ginobili and Tony Parker when both were relatively unknown players in the European leagues. Unless they can duplicate that success with their frontline personnel, they may be in for a dip next season.

That would suit the Mavericks just fine, but they may not be in good position to capitalize on their rival’s tumble. Dallas also made a dubious move this off-season, sending swingman Marquis Daniels to Indiana for reserve center Austin Croshere. Other than a salary dump, the only rational explanation for this one is that they expect to see Miami in a playoff series sometime soon and want to have as many fouls as possible to use against Shaquille O’Neal.

Uh, fine, but the Finals are over, Miami won.The most likely scenario next season is that the Mavericks will play the Heat twice, with both meetings occurring in the regular season (there’s been only one Finals rematch in the last 15 years). Yet for those two meetings, Dallas has weakened an area of limited depth: bench scoring. Daniels filled in capably for Jerry Stackhouse in Game 5 of the Finals. Stack turns 32 next season, and is a free agent in the summer of 2007. Meanwhile, the Mavs now have enough reserve pivotmen to field a team of them.

Rather than analyze their weaknesses (the Spurs were a poor rebounding and foul-shooting team and Dallas was foul prone and failed to clean the defensive glass) and shore them up, both teams have chosen to fortify themselves in case the spring of 2006 rolls around again.

This brain cramp among the Texans opens the door for the Phoenix Suns, who have sat out the off-season so far (though rumors persist that they are interested in journeyman guard Eric Piatkowski), and for the Los Angeles Clippers.The Suns won 54 games with minimal contributions from all-star center Amare Stoudemire, who’s off to a great start in the Las Vegas summer league after missing all but three games last year after two knee surgeries.The Clippers won 47 games, and though it still feels strange to say it, they figure to improve thanks to the youth of several key contributors.

Last season the Spurs and Mavericks engaged in a race for home court that resembled Affirmed and Alydar in the 1978 Belmont — two competitors racing neck and neck, far ahead of the field. Unless the Texans change the pace of their off-season, this season’s race in the Western Conference could be a more conventional one, with three or four teams battling for the top.

mjohnson@nysun.com