Representatives of 174 medical marijuana dispensaries have filed notices with the Los Angeles city clerk, indicating that they intend to remain open. City officials now face the daunting task of determining whether those stores qualify to operate under the new ordinance. The stores are among 187 that registered in 2007 to continue to operate when the City Council adopted a moratorium. All other dispensaries in the city were required to stop selling marijuana June 7, when the ordinance became effective. City officials estimate there are about 400 illegal dispensaries. Many, however, have sued the city to challenge the ordinance and some have remained open in defiance of the law.