First-round bids for NYC's Sony Tower due on Monday

NEW YORK (Reuters) - First-round bids for Sony Corp's U.S. headquarters were due on Monday, in one of the most watched sales of a Manhattan office building this year.

The 37-story, 800,000 square-foot Sony Tower is expected to fetch between $800 to $1,000 a square foot, according to two real estate sources, who asked not be named because the bidding process is ongoing.

Sony is expected to move out of the building over the next three years, leaving the new owner to find tenants.

The tower at Madison Avenue between 55th and 56th streets was built as the headquarters of what was then the world's biggest corporation, telephone company AT&T Corp. The building was completed in 1984.

Sony bought the building in 1992. Twenty years later, the Japanese company's market value has declined and last month ratings agency Fitch its debt to "junk" status, which could push up its borrowing costs and make asset sales more attractive.

In an email on Monday, Sony declined to comment on the building's sale. A source said three weeks ago that Sony wanted the building sold before it reports its financial results in March.

(Reporting By Ilaina Jonas)