Developer Bill Rudin is plotting the redevelopment of 55 Broad St. into a new, modern mixed-use tower, The Post has learned.

Prompted by the diversification of downtown and a residential population beginning to pay top dollar for apartments, sources say the third-generation developer has already hired FXFOWLE to research the feasibility of redeveloping the current 35-story, 402-feet-tall office structure into a 53-story, 742 feet-tall mixed-use building.

Such a building could include retail, technology-focused office space and ritzy apartments in an energy-efficient tower designed for the prominent site on the northeast corner of Broad and Beaver streets.

Coincidently, Cushman & Wakefield is marketing 45 Broad, the adjacent stalled site to its north, where Robert De Niro once planned a hotel. That site can host a tall but slender tower with views to the Statue of Liberty because there are no height restrictions in the area.

But it is entirely possible that Rudin is planning a tower play and will be bidding with an eye on winning that site and incorporating its 264,200 square feet into Rudin Management’s 55 Broad, so he can add a new majestic skyscraper to the downtown skyline.

The current building, also known as the NY Information Technology Center, was originally developed by Sam, Jack and Bill’s father, Lew Rudin, in the early 1960s as the headquarters for Goldman Sachs before being occupied by Drexel Burnham.

After Drexel went bust, the building sat vacant from 1990 to 1995, during a time when downtown had a vacancy rate pushing 25 percent.

No one returned calls for comment.