While third baseman Bill Mueller braces for the possibility this weekend that he will be walking across the field from the Sox'clubhouse to the visitors' clubhouse, talks were ''stalled" yesterday on a potential deal that would send Mueller to the Twins for lefthanded reliever J.C. Romero, according to a source close to the negotiations. Various permutations of that deal have been discussed, including a wider scenario in which Millar would also be dealt to the punchless Twins, with pitcher Kyle Lohse coming to Boston. But the Twins supposedly refused to include Lohse in the deal. Another starting pitcher, Joe Mays, also has been proposed.