A shaggy dog book from the First Lady, who proves here that it's a dog's life--at least at the White House--by purporting to present the dictated memoirs of Mildred ""Millie"" Kerr Bush, the First Family's young, favorite pooch. ""Our life at the White House is pretty heavily schedulized,"" Millie tells us, cueing us in to this lighthearted book's thrust: a tour of White House quarters and life with ""Bar"" and ""The Prez""--from a dog's point of view, of course (""There are some wonderful beds. in the White House on the second floor. I have tried them all""; on the day a rat surfaced in the White House pool, ""Thank heavens The Prez was there and stayed cool. He put in the pool scoop and got the rat in the net and did him in""). It's all very inoffensive and nice and about as substantial as a campaign promise; but all proceeds go to the Barbara Bush Foundation for Family Literacy, and the 136 color photographs--some seen-help beef up the lean text.