In a hard-earned triumph for Larry Silverstein, German bank WestLB has leased the top three floors of 7 World Trade Center. The firm will move from 1211 Sixth Ave. into 129,000 square feet at the 52-story downtown skyscraper.

The deal is a huge psychological boost for Lower Manhattan and one of the largest relocations there from Midtown by a major financial firm since 9/11.

WestLB's lease brings 7 WTC's 1.7 million square feet to 83 percent occupancy. When the tower opened in spring 2006 with only a single small tenant, it was widely derided as a flop.

Among its detractors was Mayor Bloomberg, who said in 2005 that Silverstein - who was asking $50 a square foot as it was under construction - should charge "the going rate" for downtown, which was $35 a square foot at the time.

But Silverstein lured Moody's and other firms at $50 a foot and up, despite abominable conditions nearby.

HSBC appeared poised to take the remaining floors at the top until the recent financial markets collapse.

Undeterred, Silverstein started talking to WestLB - as The Post first reported on Oct. 21.

Sources said WestLB's starting rent is "north" of $70 a square foot and the total rent more than $150 million over 15 years.

Newmark Knight Frank represented WestLB and CB Richard Ellis worked with Silverstein.