NEW YORK – It’s official: Bill Belichick, one of the most successful coaches in modern sports history, is a cheater.

NFL commissioner Roger Goodell delivered his much-anticipated decision on Thursday night on the “SpyGate” scandal, ruling that the Patriots’ coach was the mastermind of an illegal videotaping operation in Sunday’s 38-14 victory over the Jets. Goodell handed down a three-pronged punishment:

Belichick was fined $500,000, the maximum amount under the league’s constitution and by-laws. The Patriots were stripped of their first-round draft pick in 2008 if they make the playoffs, or second- and third-round picks if they fail to reach the postseason. The Patriots also were fined $250,000.

Goodell, in a statement, indicated that he considered a suspension for the three-time Super Bowl champion coach, but decided against it because he believes the maximum fine and draft-pick penalty is “more significant and long lasting, and therefore more effective than a suspension.”

Even if the Patriots qualify for the playoffs, they still will have a first-round pick in 2008, a choice obtained from the 49ers in the last draft.

In a letter to the Patriots, Goodell wrote, “This episode represents a calculated and deliberate attempt to avoid longstanding rules designed to encourage fair play and promote honest competition on the playing field.”

Goodell didn’t say whether he considered a forfeit, a ruling that would’ve delighted Jets fans, but he believes the Patriots’ use of a video camera “had no impact on the outcome” of the game. The camera was seized before the end of the first quarter, he said.

In a matter of days, Belichick has gone from gray hoodie to corporate hood, a stunning turn of events that taints the Patriots’ recent dominance. In an era of competitive balance, they were hailed as the model franchise, headed by a coach revered for his strategic brilliance. But in recent days, it has all come crashing down, with players and coaches around the league questioning the legitimacy of some of the Patriots’ biggest wins.

Eric Mangini, Belichick’s estranged protege, played an instrumental role in busting the Patriots. Mangini, who worked under Belichick in New England, was aware of their sign-stealing tactics and told members of the Jets’ organization last year, sources have told the New York Daily News. Armed with an insider’s knowledge, the Jets seemingly were intent on catching the Patriots, coming close last season, a source said.

The Jets released a statement on Thursday night that said little: “We support the commissioner and his findings. The focus of our organization remains on the upcoming game against Baltimore.”

In recent days, Mangini declined to comment on the league investigation, calling it a league matter. Privately, several players believe the Patriots may have benefited from stealing their signs in the game.

As of Thursday evening, the Patriots had not issued a response to Goodell’s blockbuster ruling.

On Sunday, a Jets security official apprehended Pats employee Matt Estrella on the sideline and confiscated his camera and tape, which showed the Jets’ defensive coaches giving hand signals to players on the field. A heated dispute ensued in the tunnel of the stadium, with New Jersey state troopers arriving on the scene. The camera and tape were sealed in a box and forwarded to the league office.

Some close to the Jets-Patriots rivalry believe Mangini was determined to nab Belichick, his mentor-turned-enemy. “Yeah, and that’s (messed) up,” a person with knowledge of the situation said on Thursday. “Eric should not have done that.”

Before the season, the league sent a memo to every team, warning them, “Videotaping of any kind . . . is prohibited on the sidelines.” Many believe the edict was directed at the Patriots, who had raised suspicions in recent years.