A FEDERAL judge has approved Delta Air Lines' $1.7 billion proposal to acquire some of Pan American World Airways' most coveted assets and to help Pan Am reorganize its debts.United States Bankruptcy Judge Cornelius Blackshear Aug. 12 heard testimony from Delta, other interested parties, and the federal government. Pan Am chairman Thomas G. Plaskett said Pan Am will retain 6,900 employees, down from 22,000; Delta will hire 6,600. The hearing began just hours after Pan Am's unsecured creditors agreed to a new $1.7 billion offer from Atlanta-based Delta. Delta agreed to finance a reorganization of Pan Am. The pared-down Pan Am will operate its Latin American division and Miami maintenance base. Delta will acquire Pan Am's North Atlantic routes, the Pan Am Shuttle, and its Frankfurt hub.