Remember the days when the New Orleans Saints boasted one of the league’s best defenses? It’s nothing more than a distant memory these days.

The defense is the primary reason why the Saints, for the second year in a row, get to watch the Super Bowl at home.

The statistics are uglier than Communist architecture. The defense was soft against the run (third worst in the league, giving up five yards per carry) and even worse against the pass.

How bad was it? The Saints gave up a league-worst 14 pass plays of 40 or more yards in the regular season. They also were third worst in passing yards surrendered per game, giving up 259.8.

It’s little surprise that the Saints allowed defensive coordinator Gregg Williams, known as “Dr. Heat,” to check out and move his practice to St. Louis to rejoin his old employer Jeff Fisher.

Considering his nickname, the heat delivered by the Saints was lukewarm at best. The Saints were tied for 19th in sacks with 33, a piddling figure. Even worse is that strong safety Roman Harper led the team with 71⁄2 sacks.

They forced just 26 takeaways, ranking near the bottom of the NFL after forcing a league-best 41 in 2009.

The final four minutes against the San Francisco 49ers was a microcosm of the Saints’ season. The defense allowed the 49ers to march easily down the field and score on a quarterback power play. While 49ers quarterback Alex Smith is decently mobile, the breakdown and failure to recognize the play was inexcusable. But after Drew Brees bailed the defense out with a legendary drive, the final 1:36 was the cruelest blow.

The 49ers had 90 yards of field in front of them with one timeout, needing a touchdown to win. Tough job, right?

Not if you’re going up against the Saints’ defense. Smith, with the help of matchup nightmare Vernon Davis at tight end, carved up the Saints’ secondary as if it were populated with cardboard cutouts.

The playoff thud capped what should be a busy offseason for the team.

In addition to Williams’ departure, the Saints are facing big decisions in free agency. Brees, wideouts Marques Colston and Robert Meachem, Pro Bowl offensive guard Carl Nicks, defensive tackles Auburayo Franklin and Shaun Rogers, and cornerback Tracy Porter are at the end of their contracts. The team has $94 million committed to 2012 against the $120 million cap. While there is room to re-up Brees and a few others, the chances of bringing aboard a marquee free agent on the defensive side is slim.

The good news is this year’s draft will be well-stocked with plenty of great defensive players. The biggest upgrades the team needs are in the linebacking corps, which with the exception of aging Jonathan Vilma, has been average at best. The defensive line is populated with a ton of high draft picks — like last year’s first rounder, Cameron Jordan — that haven’t lived up to their billing. Anything would be an improvement over 151⁄2 sacks as a unit, pathetic production by any stretch.

The secondary could also use an overhaul. Porter is a decent cover corner, but will be a free agent this season. Roman Harper is excellent at run support and as a pass rusher, but struggles mightily in coverage. Cornerback Jabari Greer is better suited to nickel and dime duty rather than an every-down role.

The bottom line is that the Saints have to upgrade their defense before their championship window with Brees in his prime closes forever. In the words of Elvis Presley, it’s now or never.