Unusual cold and a sharp loss of ozone in the Arctic stratosphere over the winter just past have heightened concern that changes in global climate may delay recovery of the earth's partly depleted ozone layer, scientists said yesterday. In three of the last five winters, stratospheric temperatures in the Arctic were lower and more persistent, and covered a wider area, than at any other time in the last 20 years, said Dr. Ross Salawitch, an ozone researcher at the Jet Propulsion Laboratory in Pasadena, Calif., who was one of hundreds of American and European scientists from many institutions involved in the recent Arctic survey.