Kmart Corp yesterday received court approval to start closing 283 stores as part of its bankruptcy filing. Depending on location, store sales will continue for two to three months. All stores being closed by the end of June, with the loss of 22,000 jobs. The retail value of the merchandise in the closing stores is estimated at between $1.2 billion and $1.3 billion, and Kmart expects the closures to boost its cash flow by about $550 million in 2002 and by $45 million a year after.