Prices advanced on Wall Street today after the first economic report of the year indicated the manufacturing sector remained weak in December. The Dow Jones average of 30 industrials was up 21.12 to 2,774.32 as of 2 p.m. EST. Advancing issues were ahead of decliners by a margin of about 3 to 2, with 927 stocks rising, 575 falling and 424 unchanged on the New York Stock Exchange. Volume on the Big Board came to 101.68 million shares in midafternoon. Stock prices rose after the National Association of Purchasing Management said its monthly survey of its members indicated that growth in the manufacturing economy slowed in December. The Purchasing Managers Index registered 48 percent in December, up from 46.6 percent in November, but it was the eighth straight month that the index has indicated weakness in the industrial sector. Analysts said the stock market, which had fallen in early trading in anticipation of the report, was reassured by the results of the survey. Traders believe the Federal Reserve is more likely to nudge interest rates lower if the economy is weak. Prices also were boosted as institutional investors, flush with cash after liquidated some of their holdings at year's end, went on a buying spree. Blue chip issues were among the biggest beneficiaries: IBM rose 2} to 96~ and Ford Motor was up 1&lsqb; at 44}. Toys R Us was up 2&rsqb; to 38\ after the retailer reported its Christmas sales were up 22.7 percent from a year earlier. Manufacturers Hanover led the NYSE's most active list, rising 1 to 34&lsqb;. The NYSE's composite index of all its listed common stocks was up 0.80 at 195.84. On the American Stock Exchange, the market value index rose 1.08 to 379.08.