By Pete Schroeder WASHINGTON (Reuters) -U.S. stocks and oil prices jumped on Monday as investors kicked off the final quarter of the year with a close eye on any potential economic slowdown. All three major U.S. stock indices were up in midday trading, with the Dow Jones Industrial Average surging 2.09%. The S&P 500 was up 1.88%, while the Nasdaq Composite added 1.44%. The MSCI world equity index, which tracks shares in 45 nations, was up 1.485%. Stocks rose after a brutal third quarter of steep declines. New data showing U.S. manufacturing activity grew at its slowest pace in nearly 2-1/2 yea…