The Securities and Exchange Commission, saying that it feared being accused of insider trading itself, said yesterday it has decided not to sell the stock it obtained from Ivan F. Boesky as part of the settlement of the Wall Street arbitrageur's insider trading case.

The commission said it feared that if it sold the stock and then the shares lost value because of information turned up in the SEC investigation, the commission could be accused of withholding pertinent information from the buyer.

The decision came a few weeks after it was reported that the value of the shares -- put at $50 million when the commission received them last November -- has declined to $37 million. The commission yesterday declined to comment on the shares'current worth and would not speculate what impact its investigation might have on the stock.

"The commission's action regarding the shares was based upon the public policy underlying prohibitions against insider trading," SEC Chairman David S. Ruder said in a statement. "After reviewing the present status of Boesky-related matters, the commission determined that, given the many uncertainties involved in its ongoing investigations, it was best to terminate attempts to sell the shares."

However, Ruder added, the action did not necessarily mean that the SEC felt that the value of the stock had changed from the original $50 million or that the value of the stock definitely would be diminished in coming months.

Boesky's attorney, Harvey Pitt, said in a statement yesterday that it was up to the commission "whether, when and for how much to sell the Cambrian and Northview stock." However, he said, he was unaware of any developments that might change the value of the stock, and he estimated that the net asset value of the Cambrian stock alone was more than $50 million.

In its settlement with Boesky last November, the SEC got $50 million in cash and $50 million worth of stock in two British investment trusts owned by Boesky -- Cambrian & General Securities and Northview Corp.

The SEC had planned to sell the hares and has been negotiating with a potential buyer for several months, according to Ruder. However, the best offer the commission had received reportedly was $37 million, from Michael Price, a Wall Street executive who runs Mutual Shares Corp., a company specializing in purchasing distressed stock issues.

At a hearing in June, Douglas Rosenthal, the escrow agent handling the proposed sale for the SEC, said the $37 million offer "is, in the view of my investment advisers, an excellent offer for this block of stock." It was not explained how the value of the stock apparently had dropped at a time when the rest of the stock market was soaring.

Ruder said in an interview yesterday that the commission had decided earlier this week to ask Rosenthal to stop negotiating for the sale of the Boesky stock because of the ongoing investigation. He said the SEC feared that information that might be produced by the commission's insider trading investigation could give an edge to several civil suits filed against Cambrian & General and Northview, and thus could diminish the value of the Boesky companies.

"The commission decided to make a thorough evaluation of the relevant legal and policy considerations, and we finally decided that the risk that this information might ultimately {affect} the value of the Cambrian & General Securities, in particular, should be borne by the U.S. government," Ruder said.

"If the commission authorizes the sale of the stock to third parties and it later turns out that there was information that we had that leads a reasonable person to the conclusion that it might have affected the purchase price, then that person might come back to us and say we withheld information," Ruder said.

A source familiar with the case said, "There are things that are not yet disclosed, and they may have some impact, and they may not." This source noted previous criticism that the SEC had moved with too much haste on some parts of the Boesky settlement and suggested that the commission, under recently appointed Ruder, might now decide to be more cautious in the handling of the case. "Just in terms of the image of the agency, I assume they determined that it was more important that they do not do something for which they might be criticized," the source said.

Ruder said, "I simply think that it's a matter of being cautious now and being aware of a continual flow of information that's coming in here."

Should the value of the shares prove to be less than $50 million, it is not clear whether the SEC would be able to go back to Boesky and force him to make up the difference. Boesky's attorneys have said the commission cannot do that under terms of the settlement, but an SEC spokeswoman declined to rule that out as a possibility yesterday