Financier Carl Icahn offered to buy Nabisco Group Holdings Corp. for about $5.2 billion, a day after the company said it may sell itself or its stake in the maker of Oreo cookies and Ritz crackers. Icahn said he offered $16 a share, a 29% premium to Monday's closing price, if Nabisco Group were to agree to the sale. The company controls 80.6% of Nabisco Holdings Corp., the No. 1 U.S. cookie and cracker company. Nabisco Group on Monday rebuffed Icahn's earlier offer to buy 100 million shares at $13 each as inadequate. The new bid is the biggest yet for Icahn, who has tried four times in five years to gain control of the company. "This is an offer that the board has to respond to," said Tim Ghriskey, a senior portfolio manager at Dreyfus Corp., which held 277,400 shares in December. A spokesman at Nabisco Group declined to comment. Icahn holds about 31 million shares, making him the largest noninstitutional holder. Last month, he nominated a slate of directors for the Parsippany, N.J.-based company. Shares of Nabisco Group Holdings rose $2.13 to close at $14.50 on the New York Stock Exchange before trading was halted. Nabisco Holdings Class A shares rose $6.63 to close at $39, also on the Big Board.