The ultimate sales price will be a telltale sign of confidence in the market as 2008 approaches, and multiple real estate sources familiar with it say the tower, with a distinct shiny green glass curtain wall, seems poised to fetch somewhere in the range of $750 million to $800 million.

That would make 650 Madison one of the more expensive property sales of 2007, as the 600,000-square-foot tower would sell for between $1,250 and $1,333 a square foot.

Just a block north of Harry Macklowe’s GM Building, it sits in a highly desirable midtown site, and was once eyed by Donald Trump for a castlelike condo tower, complete with a moat and a drawbridge, according to a 1984 article in The New York Times.

A sale will mark the end of more than two decades of ownership by Hiro, which first came to the New York scene in the early 1980’s, and which stuck around as many other Japanese firms pulled out of New York amid the recession a decade later. The company first picked up 650 Madison for a reported $105 million in 1984, and soon after added a tower to what was then just a bulky base of eight stories.

Hiro’s last building purchase was in 1987, according to the company’s Web site, and it holds just four properties in the city.

Sources familiar with the sale say the company seems eager to turn the tower around for a quick transaction. A representative from Hiro did not respond to requests for comment, and a broker at JPMorgan Chase, which is handling the sale, declined to comment.