Looking up a local company in the phone book isn't as easy as you might guess.

The headquarters of Crown Books can be found amid a dozen or so listings for individual Crown Books stores in the Prince George's County white pages with nothing to distinguish it from the store numbers -- unless you happen to know the headquarters is on 75th Avenue in Landover.

Then there's Dulles-based Presidential Airways, which has reservations and cargo numbers in the Northern Virginia book, but no corporate headquarters listing.

The District's Riggs National Corp. also isn't listed, although you can find it by trying the "For Dept. or Info Not Listed Above" listing under its subsidiary, Riggs National Bank.

And D.C.-based MCI Communications Corp.'s main number also is tricky to find -- it's listed in the District phone book as MCI Telecommunication Corp.

And one of the hardest local corporate headquarters numbers to find in the White Pages is that of the phone book's publisher, C&P Telephone. The number for C&P's "general office" can be found only if you let your fingers do the walking through the agate type among the listings for the company's District business offices.