(MONEY Magazine) – While a whole is often worth more than the sum of its parts, in the case of a stock, Shearson Lehman Hutton is hoping the opposite may be true. In December the firm introduced the ''unbundled stock unit.'' It slices a share of common stock into three securities: a 30-year deep-discount bond that pays interest equal to the company's current dividend; a share of preferred stock that will yield any future increase in the dividend; and an equity appreciation certificate that captures any capital gain. If the Securities and Exchange Commission approves the proposal, the trio is expected to trade separately or in combination on the New York Stock Exchange. Four major corporations -- American Express, Dow Chemical, Pfizer and Sara Lee -- have announced plans to replace 7% to 20% of their common stock, worth more than $5.5 billion, with the new securities, and other concerns are watching with interest. If the tactic works, analysts say, a participating company could win big tax breaks, some protection against takeovers, and higher earnings per share (partly because there would be fewer shares outstanding). The initial reaction on Wall Street is that the new securities will mainly interest tax-exempt institutional investors. ''This is of no benefit to the individual,'' says Jim Rogers, the supertrader, now a Columbia University finance professor, who parlayed a $600 stake into $14 million in the '70s. His reasons: Shareholders who agree to exchange their shares for units must pay taxes on any capital gain in the stock. Holders of the bonds must pay taxes annually on the increase in the bonds' value, even though they may not realize the gains for 30 years. And none of these stock particles gives investors voting rights. Existing stockholders who keep their shares will probably benefit from the swaps. ''We would encourage investors to stick with such a stock,'' advises Geraldine Weiss, editor of the newsletter Investment Quality Trends. The higher earnings, she says, would tend to raise the prices of the shares outstanding.