P213 ORACLE 213 Sun17 Oct ITN 2211:01   PECKHAM SET FOR  VITAL BY-ELECTION Campaigning in the crucial Peckham by- election starts in earnest this week with the reputations of both Labour and the Social Democrat Parties at stake. Labour, which held the seat in 1979 with a 10,800 majority, will be desperate to retain it on October 28. But Peckham is also a constituency where the Liberal-SDP Alliance must make inroads to maintain credibility. Most of the Alliance big guns will be in Peckham during the campaign. A recent NOP poll put Labour ahead with 58% and the Alliance and Tories trailing with 21% each.