If Charlie Brown moved to New York's East Village, grew a goatee, and started playing bongos in a synth-pop rock band, he still wouldn't be cool enough for Liquid Television, MTV's new weekly half-hour animation series. The show's June 2 premiere introduced such cutting-edge cartoon serials as Soap Opera (starring real bars of soap), Aeon Flux (following the ultraviolent adventures of TV's bloodiest cartoon superhero), and Stick Figure Theater (featuring scenes from classic movies performed by stick-figure drawings). Each is produced by MTV and Colossal Pictures, the San Francisco graphics studio that has been making the music network's animated station-identification segments since 1981. ''We knew our audience loved the 10-second spots Colossal had been doing for us, so expanding to a larger format made a lot of sense,'' says Judy McGrath, MTV's senior vice president and creative director. ''Liquid TV doesn't try to be The Simpsons. It's got its own identity fast-paced, funny, not completely polished. It's a real comfortable fit for us.'' The toonsters behind the show agree: ''It's part fun house, part laboratory experiment,'' says co-executive producer Japhet Asher. ''It's a mix of dozens of different animation styles. There's never been a TV show quite like it before.''