The city will spend nearly $33 million a year to lease roughly one-third of one of the office towers being built at the World Trade Center site, officials said Friday.

Mayor Michael Bloomberg's office said site developer Larry Silverstein told the city last month that he was exercising his option to make the city government take on the 14 floors of office space at a yearly rate of $56.50 per square foot.

The city had agreed in 2006 to take the space if Silverstein wanted as part of an effort to spur stalled construction at the site.

The tower is expected to be completed in late 2013, but the city doesn't expect to move in until the following year.