The 18-floor office tower that houses The Inquirer, the Philadelphia Daily News, and philly.com is up for sale for the second time in nearly four years.

Philadelphia Media Network Inc., owner of the two daily newspapers and online portal, has retained the Center City real estate brokerage Binswanger to handle the sale of the 526,000-square-foot building, at 400 N. Broad St.

Bids on the building, as well as the five-level, 502-space parking garage at 15th and Callowhill Streets and adjacent 200-space surface lot, are due by 4 p.m. June 27, according to bidding instructions on a Binswanger website.

The building was last put on the market in August 2007 by then-chief executive Brian Tierney. Patriot Equities L.P., of Wayne, had agreed to buy the property in February 2008, but the sale never closed.

This latest effort to sell the building, which was built in 1925, comes nearly eight months after The Inquirer, Daily News, and philly.com emerged from bankruptcy under new ownership.

Should Philadelphia Media Network sell the building (by Sept. 16, as the bidding documents say), it could mean that the nearly 800 journalists, advertising representatives, and other employees on North Broad Street would move to another location.

The bidding instructions state that Philadelphia Media Network "is making plans to vacate the property in the second half of 2012 and would expect to occupy portions of the building until that time."

Greg Osberg, chief executive officer and publisher of Philadelphia Media Network, said the company "would only plan to vacate our building once it becomes sold. Until that occurs, we have made no plans to leave or relocate."

Why try to sell the building now? "A significant percentage of our building is currently not being utilized, and that resulted in our interest to better understand the value of the property," Osberg said.

There is no offering price. "If we decide that an attractive value can be identified through the bid process, we will then sell the building," he said.

The last major relocation of the newspapers' operations came in 1992 when the $299.5 million Schuylkill Printing Plant opened in Upper Merion. The former pressroom and the mail room underwent substantial renovation, and the newsrooms of the two papers were moved into the renovated spaces in 1997.

Owners of Center City office towers appear to be testing the commercial real estate market. Staff writer Joseph N. DiStefano's "PhillyDeals" column reported this week that Apollo Global Real Estate put the Curtis Center and Public Ledger Building on Independence Mall up for sale last week.

Contact staff writer Mike Armstrong at 215-854-2980 or marmstrong@phillynews.com. Read his blog, "PhillyInc," at www.phillyinc.biz.