When it was confirmed that the Phoenix Suns had dealt All-Star caliber forward Shawn Marion and reserve guard Marcus Banks to the Miami Heat for aging center Shaquille O’Neal, my jaw hit the floor. This is one of the dumbest trades that I’ve ever witnessed — and remember, I write often about Isiah Thomas’s various foibles with our Knicks.

The deal guts the nucleus of the Suns, a team that has an average of 59 wins per season since assembling its current core. That core is on pace for — surprise! — 59 wins this season, too. Why destroy that nucleus to make the team older, more expensive, and less athletic? Let’s look at O’Neal and Marion on the basis of their production. Marion is 29, averages 15 points and 9.9 rebounds per game, plays 36 minutes per contest, and shoots 52.6%, 34.7% from behind the arc. Oh yeah, and Marion is durable: Since becoming a starter in 2000, he’s missed 12 games, and never more than three in a season. Marion makes $16 million this season, and will make $18 million next season, which is the final year of his contract.

Meanwhile, let’s discard those romantic notions about how wonderfully athletic O’Neal was in his youth. Unless the Suns have invented a very special anti-aging machine, this is the player they are getting: O’Neal turns 36 in four-weeks, he averages 14.2 points and 7.8 rebounds, plays 28 minutes per contest, and shoots .58.1% from the field. Durability has been an issue with Shaq: He missed 23 games two seasons ago, and 42 last season. He’s due to make $20 million this season and next, and $20 million more in 2009-10 — when he turns 38.

Just on that data alone, one shouldn’t trade Marion for O’Neal. But there are other factors to consider. O’Neal is a poor fit for the Suns’ up-tempo offense. In his younger days with Orlando and on a few of the Lakers’ title teams, O’Neal played on teams that finished near the top of the league in Pace Factor, which measures possessions per game. Since his move to Miami four seasons ago, he’s been much more comfortable with a slower-paced game.

Another factor is how he will mesh with the Suns’ other big man, Amare Stoudemire. O’Neal’s addition would move Stoudemire to the power forward spot — perhaps a better fit for his physique, but not for his game. One of the Suns’ most effective plays is the high pick and roll. Stoudemire sets the pick for point guard Steve Nash near the 3-point line, then rolls quickly toward the basket. Usually teams either follow Stoudemire, leaving Nash wide open for a 3-point shot (and Nash is nailing an otherworldly 46.8% from way downtown), or Stoudemire gets a step on his defenders, leading to a pass and a thunderous dunk. With O’Neal clogging the middle, Amare is likely to find Shaq’s defender in the lane, feet carefully placed outside the restricted area, ready to absorb the collision that will result in an offensive foul on Stoudemire. It could well lead to a scenario such as the Eddy Curry and Zach Randolph-clogged middle problem in the desert.

Another key problem from this trade would be on the boards. As shown from the stats cited above, Marion, though the shorter of the two players, is at this point in his career a substantially better rebounder than O’Neal. That difference will be exacerbated when the Suns use Boris Diaw on the frontline. Diaw nearly matches most of Marion’s offensive stats, but his rebounding isn’t close. The Suns are already one of the weaker rebounding teams in the league, and this move won’t help.

So not only does this trade affect the team’s age, athleticism, and cost, it also threatens the core of their offensive design and diminishes them further in their weakest area — rebounding. What could possibly motivate such a move?

Panic is the answer. The Suns lost 84–81 to the Spurs sans Tony Parker last Thursday in what was supposed to be a big revenge game for Phoenix. It was their first meeting at U.S. Airways Arena since the two teams met in the playoffs last season. Then on Friday, the Lakers — a team that has manhandled the Suns twice this season — got bigger still with the acquisition of Pau Gasol. It’s likely that an order came from owner Robert Sarver to make a countermove quickly, and this is the first one that came along.

The last time the Suns faced adversity over team height was when Stoudemire underwent knee surgery and missed almost all of the 2005–06 season. Their response was to go even smaller, and they won 54 games and made it to Game 6 of the Western Conference Finals before flaming out. This time, their response has been very different, and it may herald a decline in power of coach Mike D’Antoni. D’Antoni’s small ball Suns were the most interesting NBA team of the last 10 years. The acquisition of O’Neal effectively ends that era, and it’s for no better reason than a mere desperate attempt to keep up with the Joneses.

mjohnson@nysun.com