Senior Obama administration officials, newly joined by state attorneys general, were on the brink Thursday of finalizing major elements of a possible settlement with large U.S. banks accused of flawed and fraudulent foreclosure practices, sources familiar with the discussions said. But absent from this otherwise united government front, which is preparing to submit a proposed settlement to financial firms within days, is the regulator of the nation's largest banks, the Office of the Comptroller of the Currency. The OCC has raised concerns that the firms might be required to pay too large a fine - $20 billion or more - and adopt mortgage procedures that the agency doesn't think make financial sense.