The economy showed more healthy signs of recovery. In a survey of 250 industrial companies, the National Association of Purchasing Management said the number of purchasing managers reporting an increase in new orders was the highest since 1977. Last week, the Labor Department reported a slight decrease in the unemployment rate for March - from 10.4 to 10.3 percent. And according to the Commerce Department, builders kept up their heavy spending on construction materials and labor in February. They also established a record $25.3 billion for office construction that month, it said.