WASHINGTON, Sept. 26 — With six weeks to go, Republicans appear to hold a slight edge in this year's fight for control of the House, according to interviews with politicians and analysts around the country and examinations of local polls. Republicans have about 10 more seats safely in their hands than the Democrats do. So even if they won fewer than half of the approximately 40 races that are truly competitive, they could still keep control of the House. That unusually small number of competitive districts means that the Democrats have fewer opportunities to achieve the net gain of seven...