UPDATE 1-U.S. 30-year mortgage rates fall to lowest in six weeks -Freddie

(Adds details, graphic, table) Jan 12 (Reuters) - Interest rates on U.S. 30-year fixed-rate mortgages fell to their lowest levels in six weeks, in step with the decline in U.S. government debt yields, mortgage finance agency Freddie Mac said on Thursday. The borrowing cost on 30-year mortgages, the most widely held type of U.S. home loan, averaged 4.12 percent in the week ended Jan. 12, it said. Last week, 30-year mortgage rates averaged 4.20 percent. Two weeks earlier, the rate was 4