CHRISTIE'S International, the auctioneers, says it plans to cut about a tenth of its work force in London following a 50 percent drop in its autumn season sales . . . TWO BROTHERS were shot to death while renovating a store in Gary, Ind., bringing to seven the number of shotgun slayings believed carried out by the same man since October, police said . . . MORE THAN 1,000 people a day are flocking to the back of an auto parts store in Progreso, Texas, to see what many believe is an image of the Virgin Mary on the bathroom floor.