The exterior of Arnold & Porter’s current building on 555 12th Street NW. (Tom Allen/The Washington Post)

So for office developers and office leasing agents in the District, Arnold & Porter, which is acquiring California law firm Howard Rice, has become the proverbial white whale of the leasing world at the moment.

According to a number of development and leasing sources, who asked to speak anonymously because they are not authorized by the firm to discuss its search, Arnold & Porter is weighing a number of options. Here are three: remain at 555 12th Street, owned by Manulife; move to CityCenter DC, currently under construction by Hines and Archstone; or move to a new office building that Boston Properties plans to build in replacement of the National Public Radio headquarters at 635 Massachusetts Ave. NW.

Arnold & Porter itself declined comment.

For a couple of reasons, Arnold & Porter’s decision could have an outsized effect on Washington’s real estate market. First, there are so few other large tenants that can anchor new construction right now that developers like Hines and Boston Properties are probably particularly eager to land them.

But with the changing needs of law firms, and their ability to squeeze into much smaller spaces in new buildings with modern floor plans, the pressure may be even greater on Manulife to retain them. With the new layouts being offered in more modern buildings, older space for law firms is becoming harder and harder to fill. Example A is the space that the firm Howrey vacated at 1299 Pennsylvania Avenue NW (owned by Vornado/Charles E. Smith) when it dissolved.

Example B could be Arnold & Porter.

Follow Jonathan O’Connell on Twitter: @oconnellpostbiz