FEDERAL RESERVE, REACTING TO SIGNALS OF A SLOWDOWN, CUTS KEY RATE HALF A POINT
Federal Reserve, in surprise move, cuts federal funds target rate to 6 percent, from 6.5 percent, sending powerful signal that it seeks to prolong economic expansion; acts between scheduled meetings, with barely disguised haste; is able to cut discount rate by only quarter percentage point, to 5.75 percent, but says it will make second cut once it gets formal request from Federal Reserve bank; signals it is likely to further cut rates in coming weeks and months; move sets off strong stock market rally, with Dow Jones industrial average rising 299.60 points, to 10,945.75 and Nasdaq composite index surging record 324.83 points, or 14.2 percent, to 2,616.69; Pres-elect George W Bush welcomes move but holds it does not reduce need for tax cut; graphs of federal funds rate and Nasdaq composite index; table of best one-day Nasdaq gains; photo (M)