If Donnie Walsh wanted a big job to confirm his reputation as one of the best NBA executives of the last 25 years, then he might have one. Cleaning up the mess at Madison Square Garden is a monster-size task, but I suspect that Walsh will be up to it if he is hired as team president. He will have a long and arduous agenda: These are the first five items I would address.

1. Fire Isiah Thomas. Today. Right now, even. Walsh needs to raise the level of professionalism at the Garden, and the first way he can do it is by changing the way dismissals are handled. Instead of the ugly twist-in-the-wind approach used with the firings of Don Chaney and Larry Brown, Walsh — or even James Dolan, since Walsh is still officially an employee of the Indiana Pacers — should inform Thomas that he will not be retained next season, and that he’s free to either coach until the end of the season or leave now and allow his assistants to run the team for the final 11 games.

2. Hire Tom Thibodeau as coach. Thibodeau, the man behind Boston’s rise as a defensive power, was Jeff Van Gundy’s lead assistant for several years on the Knicks bench (imagine how different the Knicks’ recent history might have been if he, instead of Chaney, had taken over for Van Gundy in 2001). Now, it’s easy to say that Thibodeau had Kevin Garnett to work with. But while the Big Ticket is a great defensive player, it takes more than one man. When Garnett was in Minnesota, his teams rarely finished above the middle of the pack in Defensive Efficiency (points allowed per 100 possessions). The improvement in the Celtics’ defense owes to Thibodeau’s schemes and his ability to teach them. Thibodeau is interested in a head coaching job; he interviewed for the Sacramento opening last summer.

The Knicks haven’t been a winning team since “hanging chads” were a punch line, and I don’t think that will change overnight. The team hasn’t been in the top 13 of the league defensively since then, either. I think that the Garden faithful will more easily accept the long road back if the team improves defensively. Thibodeau would be the best choice to spark that improvement. Since there is an understandable clamor to bring Mark Jackson to the organization, he might make a good assistant coach under Thibodeau.

3. Make friends with Suns team president Steve Kerr and Trail Blazers general manager Kevin Pritchard. The Knicks need a massive infusion of talent and Thomas’s dealings have already cost them a first-rounder in 2010 and two future second-rounders as well (all for the wonderful privilege of showcasing Demetrius Nichols and Jared Jordan during the pre-season — and then cutting them both). Phoenix is renowned for dumping draft picks, and they have Atlanta’s first-round pick this season. They might be willing to part with it in exchange for a future pick. Pritchard is well experienced with the joys of draft day deals with Kerr, and partially as a result, Portland is about to experience a roster surplus. The Knicks should be happy to alleviate any overcrowding in the Blazers backcourt and even have the expiring contract of Malik Rose to sweeten the pot. You might think the Knicks have an overstuffed roster too, but that brings us to the next task.

4. Break out the buyout papers. Jerome James, see ya! Jared Jeffries, best of luck! Stephon Marbury, it’s been real! It’s time to wave goodbye to some of Thomas’s biggest blunders. And in doing so, Walsh should announce that he’s ready to buy out any player who isn’t willing to work hard to turn this ship around. After all the words, Knicks castoffs should bring any player’s market value down to about zero.

5. Buy time. Denounce the notion of quick fixes as the modus operandi of the previous regime. The Knicks are not going to go from more than 50 losses to more than 50 wins overnight. Dramatic moves such as the ones above will raise expectations, so temper them. The team shouldn’t hang itself on numbers such as win totals, but it should set tangible goals. During year one, the team should turn things around and start building a defense worthy of the floor at Madison Square Garden (those words alone will win back oodles of fan support). During year two, it should start solidifying the nucleus of the next Knicks powerhouse. During year three, it should set sights on basketball in May. Goals along those lines are vague enough to be positive, without giving folks the ability to hang you with your own words.

Knicks fans will have to realize that center Eddy Curry, forward Zach Randolph, and guard Jamal Crawford are probably going to be with the team next year. They have absolutely no trade value right now, since they are members of a team that has lost almost 210 of their last 320 games. Raising the image and improving the on-court performance of the team will raise their trade value. Perhaps at the 2009 trade deadline — if not during the offseason following the 2008-09 campaign — Walsh will be able to move these players.

Turning the Knicks around isn’t going to be an easy job, but it’s not an impossible one either. The Thomas era has been so chockfull of errors that the Walsh regime will only have to apply common sense — as opposed to ingenuity — to get back on track. Once the team is liberated from its state of dysfunction, savvy personnel moves and smartly managed expectations can return the Knicks to the Eastern elite. These five moves should get them started in the right direction.

mjohnson@nysun.com