The Californians, wrote O. Henry 60 years ago, are not merely inhabitants of a state--they're a race of people; and one of the loveliest specimens of that species is 19-year-old September Playmate Dru Hart. In transition from the leisurely pace of growing up in the San Fernando Valley to the rush and responsibility of her new life as a career girl in Los Angeles, Dru manifestly embodies the effervescent enthusiasm and vitality O. Henry attributed to the denizens of that swinging state. Whether at a ball game in Chavez Ravine (she's a self-admitted baseball nut) or in the course of her hectic days as personal secretary to prominent Los Angeles attorney William Anderson, Miss September enjoys both with a native-Californian gusto. Dru--"It's short for Drucilla, which makes it obvious why I like to be called Dru"--also digs such mixed-media recreation as rock 'n' roll, surfing and water-skiing with the endless-summer set. Her notably informal speech pattern further places her firmly in the tuned-in generation: "Without making a big thing out of it, I guess I do try to groove to the fun side of life as much as possible. But, at least for me, it doesn't take a chemical or even surroundings like the Sunset Strip to flip me out. Unless the Dodgers have a big home series--I've been mad about them ever since they came to town when I was nine--I spend most of my warm-weather week-ends on camping trips with friends. We usually split for a place I discovered with my family--a long, beautifully clear lake called the Cachuma Reservoir about a hundred miles up the coast. We sleep overnight on the banks and then hike up into the hills. You're so completely detached from the city, it's easy to imagine how isolated the first settlers must have felt." Dru currently maintains a small apartment in Van Nuys, halfway between her family's home and Los Angeles, but she's looking for a larger place in L. A. "to fill with big bright paper furniture, plastic cushions and a huge stereo system." Although she's satisfied at the moment with her career as a lawyer's girl Friday, she says she might abandon the staid surroundings of law offices and courtrooms for something more glamorous. "If fashion photographers weren't quite so obsessed with tall, emaciated girls," says Dru, "I'd like to try my luck at modeling. And I'm turning on to acting, too. For some time, I've thought about joining a little theater group; I wish now that I'd taken some dramatic training in school--it would help. But I'll have to see how things turn out when I move to L. A." With what Dru has going for her, things should turn out just fine.