The pressure for RJR Nabisco Holdings Corp. to sell off its Nabisco Brands division is increasing. Bennett LeBow, who as head of Miami-headquartered Brooke Group has been spearheading the sale push said Monday he has enlisted Carl Icahn and will begin a proxy fight if RJR doesn't sell Nabisco. Mr. LeBow said he and Mr. Icahn, who together are RJR's second biggest investors, will suggest their own slate for the RJR board if the current board doesn't act. Mr. LeBow is suggesting the market value of RJR could increase 50% as a result of a spinoff. RJR so far has declined to comment.