By Ilaina Jonas

NEW YORK, Feb 12 (Reuters) - Lehman Brothers Holdings Inc has agreed to sell 237 Park Avenue, a 21-story Midtown Manhattan office building, to RXR Realty and Walton Street Capital LLC, the winning bidders said on Tuesday.

The purchase price is $820 million, two sources familiar with deal said.

The pending sale comes just months after Lehman agreed to sell its biggest property holding, apartment owner Archstone, to AvalonBay Communities Inc and Equity Residential for $6.5 billion plus the assumption of debt.

Lehman, which collapsed in 2008, emerged from bankruptcy in March 2012 and is selling assets to repay creditors.

Lehman originally was the lender to Broadway Partners, which used the $1.23 billion loan in 2007 to buy the building as part of a larger purchase of a portfolio of properties.

When Broadway defaulted on part of the mortgage, Lehman was allowed by the bankruptcy court in 2010 to buy a junior part of the mortgage for up to $255.4 million. Lehman paid roughly 85 percent of the face value of that and took control of the property.

All told, after repaying the senior mortgage and factoring the price paid for the junior slice, Lehman stands to net about $185 million. Lehman has also been recouping the payments on the junior mortgage.

The 1.25-million square foot building is on Park Avenue between 45th and 46th streets, close to Grand Central Terminal, and is 80 percent occupied, RXR and Walton Street said in a statement.

RXR, one of the biggest owners of New York City property and Walton Street, a private real estate investment company, plan to renovate the building. The plans include new entrances, a redesigned atrium and new elevator cabs. They also plan to install a new glass facade enclosure on the two top floors, allowing for floor-to-ceiling windows.