Caterpillar Inc CAT.N, viewed as bellwether for the industrial sector, fell sharply. By Noel Randewich and Ankika Biswas April 4 (Reuters) - Wall Street dropped on Tuesday after evidence of a cooling economy exacerbated worries that the Federal Reserve's campaign to rein in decades-high inflation may cause a deep downturn. The S&P 500 closed lower for the first time in a week as data showed U.S. job openings in February dropped to the lowest level in nearly two years, suggesting that the labor market was cooling, while factory orders fell for a second straight month.