If you dropped an anvil on Brendan Frasers' head, little birdies would probably start flying circles around it.  Never has an actual human portrayed a cartoon character as pitch-perfectly as Brendan Fraser played George of the Jungle.  Fraser can seem completely untouched by the grimness of humanity, and that's made him a natural to play characters not of this world.  George, Encino Man, the title role in next falls' Dudley Do-Right.        "I'm interested in characters who have a sense of discovery," Fraser said this fall from the set of Dudley.   "And I like characters who never know how or why they're making that discovery."  From his more serious turn as an ersatz Frankenstein in Gods and Monsters to his well-known vine-swinging role as George, he casts the spell of the ingénues' ingénue, the Gumps' Gump. the guy Rip Van Winkle beats to the 9 a.m. meeting.  "I guess that's why the press and others will always call me the 'naive guy,' " says Fraser rather dryly.      And if there's an alarm clock to rouse the sleeping naïf, it's Alicia Silverstone.  In the upcoming Blast From the Past, Fraser plays a man who has been locked in a bomb shelter for thirty years and emerges to face the complexities of Ms. Silverstone as well as life in the waning ticks of the twentieth century.  Along with Dudley, it is one of three films featuring Fraser (The Mummy is the third) that will be released this year---something of an emergence of his own.  Perhaps now we'll realize what Sir Ian McKellen, who worked with Fraser in Gods and Monsters, has known for a while.      "I didn't appreciate Brendans' performance while it was happening," he said recently.  "I've talked to somebody who worked with Marilyn Monroe, and [he] said the same of her.  You could only see it through the camera or on the screen."      Fraser, in other words, is made as much for Merchant/Ivory as he is for Hanna-Barbera.                                                                                                                -DEVIN FRIEDMAN