Paxson Communications chief Lowell "Bud" Paxson urged President Clinton to insist that the FCC keep March 6 as the date to auction spectrum now used for TV ch. 60-69. The spectrum is expected to be used for third-generation wireless services. Paxson, who owns 18 of the 138 stations on the band, is worried the auction will be postponed for a third time. Wireless companies expected to bid pushed the FCC to postpone the auction previously until spectrum-clearing rules are finished.