By Howard G. Chua-Eoan

These two aren't quite Laurel and Hardy, but they certainly are an odd couple. Ed Koch, New York City's mayor, is plummeting in popularity just as he's up for re-election. Jphn Cardinal O'Connor, the city's other top pol (and its Archbishop), is riding high as a leader of American Catholic orthodoxy. So what are they up to with His Eminence and Hizzoner, a co-authored volume of their opinions due to appear in bookstores this week? Close friends, they turn out to have many similar views -- except for campaigning. Koch, a Jew, hopes the book will shore up his Catholic support. O'Connor pledges churchly neutrality toward all candidates.