Want to know who's who in the Reagan White House and how to reach them? For $9 you can get a copy of the National Journal's 16-page White House Telephone Directory, which lists the names and numbers of 2,000 employes workings in the White House and executive offices. National Journal, Circulation Department, 1730 N St. NW, Washington, D.C. 20036 . . . A booklet for the disabled called, "I Think I Can, I Think I Can . . . Yes, I Can!" is available free at all Prince George's County Memorial Libraries. The booklet, published in oberservance of the International Year of Disabled Persons, lists resources, services and a bibliography of reading and reference material ... The Film Center, 938 K St. NW (393-1205) offers a 50 percent discount on the rental of 16mm feature films when the showing takes place in a private residence for family and friends. Walt Disney Productions and certain minimum rentals are excluded. You can reserve two days before pick-up date, get the films the day before the showing and return them the following day. Choose from the firm's catalog selection ... Pewter ornaments adorning the Washington, D.C., Christmas tree on the Mall are available at Woodward & Lothrop stores for $7.95 each. They depict the Lincoln Memorial, Washington Monument, White House and Capitol.