Just eight weeks after being booted from the helm of Commander in Chief (the hit show starring Geena Davis), Rod Lurie is back in the ABC fold to write and direct a pilot about an 18-year-old mayor. It's not a new idea: Several other kid-mayor stories have been unsuccessfully kicked around Hollywood lately (a TV series produced by Adam Sandler, a screenplay written by Doonesbury's Garry Trudeau). Lurie says he was unaware of the other projects, but he knows how to succeed where predecessors failed. ''I'm not going to be focusing a lot on childish things,'' he says. (Read: no ponies in the mayor's mansion.) And he's optimistic about returning to ABC. ''We made Commander the No. 1 new show of the season, and we're going to make this the No. 1 show of next season.'' Spoken like an expert politician, sir.