With just four days to go before the scheduled closing of Atlantic City’s Trump Taj Mahal, the CEO of the casino’s parent has written a letter to investor Carl Icahn begging him to step up with a multi-million dollar lifeline.

“Time is short,” Robert Griffin, the chief executive of the bankrupt Trump Entertainment, wrote in the Tuesday letter.

If Icahn and the casino workers’ union fail to reach a deal on benefits and other financial matters — and if Icahn decides not to extend a loan to keep the lights on without a deal — the Taj is scheduled to close on Dec. 20, putting 3,000 people out of work.

Icahn, the Taj’s senior lender, can keep the casino operating until the summer if he provides roughly $30 million in bankruptcy financing.

The billionaire investor is considering making the loan — but it is far from certain, sources said. Icahn owns $292 million in senior loans and would get only a partial recovery in a liquidation.

The shareholder activist has offered to convert his debt into majority ownership if the union agrees to some benefit cuts including changing the work rules.

A Delaware bankruptcy court has ruled he can break the collective bargaining agreement, and the union has appealed the decision.

Since then, Icahn and the union have not been able to broker a compromise.

Griffin, in the three-page letter, reviewed by The Post, called the casino workers’ union “callous” for not agreeing to the terms of Icahn’s bailout.

“No matter what we do, it seems that [United Here] Local 54’s leadership just will not make a deal,” Griffin writes. “At this point, they even refuse to accept terms that they themselves proposed.”

Griffin takes a swipe, too, at Marc Lasry’s Avenue Capital and the other hedge funds that actually own Trump Entertainment, parent also of the recently shuttered Trump Plaza casino.

“Our current equity owners are [not] willing to invest another penny,” the letter to Icahn explains. Griffin also says in the letter that the state and city have “abandoned” the Taj.

The CEO admits the investment is “extremely risky” because the union could win its appeal and force the Taj to pay its workers current benefits.

Icahn, who owns Atlantic City’s Tropicana, earlier this year was in talks to buy the Revel casino, but in the end did not strike a deal and the Revel shut down.