In what could become a test of the city’s Class A commercial office market, a 49 percent interest in the landmark Seagram Building is being marketed by Citibank’s high net worth unit on behalf of RFR Holding.

The parties want to push the pricing over $2,000 a square foot for the 800,000-square-foot Park Avenue tower, which would revalue it at more than $1.8 billion, Real Estate Finance & Investment reported.

A record $1,585 a foot was hit by the 2007 sale of 450 Park Ave. But while city pricing is rebounding, it is still at half that amount today. Rents at the Seagram Building are often over $100 a square foot and, according to CoStar, about 106,000 square feet is for lease.

“If you want to test the strength of the market, it’s certainly the building with which to do it,” said Woody Heller, head of capital transactions group at Studley, who is not involved in this offering.

Designed by Mies van der Rohe/Philip Johnson in 1958, the 38-story building is known worldwide for its stark plaza and international style. Its air rights were also to be transferred to RFR’s nearby stalled 610 Lexington Ave. hotel condo development, which is reported as being in the middle of a foreclosure by ING.

Aby Rosen of RFR and Citibank did not return calls for comment.

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Party City has just leased 13,000 square feet in a portion of a new retail area being developed on the plaza of 670 Columbus Ave.

Taking its first store in a decade, Party City signed a 15-year lease for the southwest corner of 92nd Street. The space includes 1,793 square feet on the ground and 11,728 on the lower level. The retailer, which already has a Manhattan store on W. 14th Street, was represented by Patrick Smith of SRS Real Estate Partners.

According to Amira Yunis of Newmark Knight Frank, who represented the building owner along with colleague Jared Lack, Party City will open in 2012. The asking rent was $150 a square foot on the ground and $75 a square foot on the lower level. An additional 23,000 square feet is available, which can be subdivided and has 200 feet of frontage on Columbus Ave.

After several years of going through numerous city agencies, building owner Larry Cohen obtained permission to build a small retail building in the plaza area of the residential tower, according to Yunis. “It’s pretty exciting and ingenious,” she said.

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Asset manager ICON Investments is moving to 3 Park Ave., where it has signed a 10-year lease for the entire 23,000 square feet of the 36th floor for its new headquarters.

The company intends to relocate from 100 Fifth Ave. later this year.

ICON was represented by Brad Needleman and Silvio Petreillo of CB Richard Ellis.

David Glassman of Cushman & Wakefield together with David Nevins and Adam Karafiol of building owner Cohen Brothers Realty Corp. handled the transaction for Charles Cohen.

Two other new deals at the 41-story building bring its occupancy to 95 percent. Asking rents in the building are in the high $40s per square foot.

Major League Gaming, represented by Gui Tepedino of Roberta Panos, leased 11,575 square feet on the 11th floor, while Prophase Training Group, represented by Alanna Martin of Green Buildings NYC, took 6,755 square feet on the 37th floor.

Marc Horowitz of Cohen Bros. worked in-house on both of these long-term deals.

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The sale of the Sagamore apartment building at 89th Street and Columbus Avenue from Related Companies to a client of LaSalle Investments closed on Friday for $140 million.

The building is an 80/20 project, with 80 percent of the units at market rents and 20 percent of the tenants with lower incomes paying less.

Investment guru Douglas Harmon of Eastdil Secured marketed the building, which was the first apartment tower to go into contract this year.

“Pricing for luxury residential rental property in the city has been and will remain strong,” said Harmon. “We are still overwhelmingly supply constrained.”

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SAC Capital has finally signed its lease at 510 Madison Ave. for 66,000 square feet on the 2nd through 6th floors, where it will move from 540 Madi son Ave. Sources report the rent will be in the high $80s per square foot. [email protected]