The state’s economic development agency has scrapped proposals to redevelop Belmont Park, including one for a 25,000-seat soccer stadium for the New York Cosmos, rebooting the long-delayed process after four years of inaction.

The Empire State Development Corp., which issued a request for proposals (RFP) in 2012 to develop the state-run land, sent letters to four bidders Friday announcing they were canceling the RFP without picking a winner.

The letters come amid reports that the Cosmos, a franchise that folded in 1984 but was revived in 2011 to play in the North American Soccer League, could cease operations.

“The Belmont Park RFP has been canceled in order to consider economic development and job creation opportunities beyond the scope of the original request,” said ESD spokesman Jason Conwall.

Conwall declined to comment on future plans for the site.

Cancellation of the request for proposals could open the door for the New York Islanders to return to Nassau. Sources told Newsday in July that the team’s new owners had met several times with officials of the New York Racing Association, which runs Belmont, to discuss a possible new arena.

Sign up for The Classroom newsletter. Education on Long Island is changing. Find out how. By clicking Sign up, you agree to our privacy policy.

The Islanders have a 25-year agreement to play at Barclays Center in Brooklyn but both the team and the arena can opt out in January 2018. An opt-out must be precipitated by “good faith discussions regarding modification of the financial arrangements,” according to documents obtained by Newsday.

Those discussions would have to take place after this season. If the Islanders opt out, they could leave after their third or fourth season in Brooklyn. If Barclays triggers the opt-out, the team would leave after the fourth season. The team is in its second season at the arena.

Islanders’ players have complained about the quality of the ice surface at Barclays while fans have been critical of obstructed-view seats. Islanders’ average attendance this season of 12,549 ranks second-worst in the National Hockey League.

An Islanders spokesman did not return calls for comment and a Barclays spokesman declined to comment.

In 2008, Elmont civic and political leaders released a “Community Vision Plan” for Belmont that called for a hotel, retail stores and equine-related businesses. A 2009 state study identified two parcels of land, totaling 36 acres, near the grandstand suitable for development. The RFP was issued in September 2012 and four bidders responded in early 2013.

The Cosmos proposed spending $400 million in private funds to build a stadium and 370,000-square-foot complex including a hotel, restaurants, and a community center.

Three other developers — Engel Burman Group of Garden City and Basser-Kaufman of Woodmere; Blumenfeld Development Group in Syosset and Related Companies in Manhattan — proposed complexes with restaurants, supermarkets and community centers.

Ed Blumenfeld, president of Blumenfeld Development, called the RFP’s cancellation “disappointing” and said the state “wasted everyone’s time.”

Steven Krieger, a partner at Engel Burman, said their plan “both met the desires and needs of the community.”

The Cosmos were successful on the field, winning NASL titles in three of the past four years. But attendance at home games at Hofstra University’s James M. Shuart Stadium dropped from an average of 6,000 fans per game last year to 3,500 in 2016, officials said.

The Cosmos’ front-office staff have been placed on a two-week furlough and most player contracts were terminated this week, said Cosmos spokeswoman Dee Kundra.

In addition, three of 12 NASL teams departed to play in competing leagues. “We are waiting on finalization of the league’s plans before making any final decisions,” said Kundra.

State Assemb. Michaelle Solages (D-Elmont), an opponent of the Cosmos stadium, called the state’s decision a “victory for the community” and said the state should solicit proposals that “create high paying jobs and protect the quality of life throughout the surrounding communities.”

State Sen. Jack Martins (R-Old Westbury) said, “It’s a shame that ESD wasted nearly four years delaying action on Belmont redevelopment only to turn around and go back to square one.”

Nassau County Executive Edward Mangano said the state should issue a new RFP to identify redevelopment ideas “that complement the community and strengthen our economy.”