"The most envied girl in America"--that's what the tabloids call Julie McCullough, 24, who plays teen idol Kirk Cameron's heartthrob on the hit sitcom Growing Pains. Julie joined the show a few months ago, cast as the Seaver family's nanny. Her gold hair, hazel eyes and gamine grin--plus the way she kept bending sexily near Mike Seaver, Cameron's hormone-crazed character--made such an impression, she was quickly signed up as a regular. "We just seemed to have that chemistry," said Kirk. The season ended this past spring with a cliff-hanger episode in which he proposed marriage to Julie. To legions of jealous Kirkomaniacs, she said, "Don't hate me. I'm only acting!" Hate Julie? Naah. "I wish I could be that girlfriend on Growing Pains," one Kirk fan told Good Morning, America, "but as long as he's happy...." Julie first made Playboy fans happy in February 1985, appearing as "thepride and joy of Allen, Texas," in The Girls of Texas. She rode a rising star on our cover that month. As Miss February 1986, laughing at the thought of Julie as beauty, she said, "I have little eyes, a mouth full of teeth and ears that I call elf ears." Her Playmate Data Sheet mentions a single ambition: to be an "actress--because you can be anything you want to be--or at least 'act' like it." Her Playboy springboard led to Star Search, which led to a guest shot as Tony Danza's fantasy girl on Who's the Boss? and a movie debut in the bullets-and-bosoms classic Big Bad Mama II. There was also a romance with TV's Scott Baio, who played Chachi on the old Happy Days series--Julie is the answer to the trivia question: "Who helped teach the facts of life to two of the tube's most eligible hunklets?"--and a couple of controversies. One involved a Texas preacher who, decrying sin, sex and Playboy, said in all seriousness, "The easiest thing to do is jump on Julie." Another rocked the sleepy town of Wilmington, North Carolina, where Julie was stripped of her crown as queen of last spring's Azalea Festival. A few Wilmington bluenoses waved her centerfold at fest officials, who promptly caved in to the Stop Julie brigade. "I was very upset and hurt," she said. She soon got over the snub. The first lady of Growing Pains has her hands full with Kirk and little room left for azaleas. A frequent guest at Playboy Mansion West, Julie keeps in touch with her Playboy roots. She once shared a Los Angeles apartment with Miss August 1986, Ava Fabian, and Miss May 1987, Kym Paige. Getting on their guest list was the dream of Southern California's male population. Julie even makes an appearance on the new Playboy pinball machine, as an all-American blonde seated poolside. When fundamentalists and floral-fest organizersscold her for going all natural in a famous men's magazine, she stands her ground. "I have nothing against sex," she told our readers. Puritans cringed; Playboy readers cheered. Julie knew even then that a girl can be wholesome and sexy at the same time. Not to mention intelligent and charming--which is how Kirk Cameron describes the Julie of Growing Pains