The corporate chess game between Phillips Petroleum Co. and corporate raider Carl C. Icahn continued yesterday as Icahn restructured his offer in an effort to cash in on a potentially lucrative defensive measure installed earlier this week by Phillips -- but Phillips said Icahn wasn't eligible for the device's benefits.

Phillips management said it continues to expect to hold a shareholders' meeting Feb. 22 to vote on a controversial recapitalization plan that Icahn opposes. Many analysts believe Icahn wants to take over Phillips in an effort to wring the most value from its assets.

Phillips stock, which had been driving higher in recent days on speculation that the company may soon be taken over by Icahn or someone else, slipped 12 cents to $49.87 in heavy trading yesterday.

Icahn said early in the day that he planned to change his offer for Phillips from $55 a share -- $8.5 billion -- for the whole company to $57 a share for 25 percent of the company's stock. But he left open a modified version of the earlier offer as a back-up.

With the approximately 5 percent of Phillips stock he already owns, the new offer could give Icahn 30 percent of the company -- enough to trigger a mechanism under which Phillips will give stockholders a warrant to swap their stock for one-year senior notes worth $62 a share. That device, put into place Thursday, is regarded on Wall Street as a "poison pill" defensive measure that would make an unwanted takeover of Phillips difficult by giving the company's shareholders a higher-priced alternative offer.

Icahn, who could not be reached for comment, said in a statement that he thought the offer "provided all shareholders with rights to receive" the $62 note -- meaning, apparently, that he could swap whatever stock he can buy at $57 a share for the $62-a-share notes.

But Phillips Chairman William C. Douce, in a letter to Icahn released by the company, disagreed. He said he found Icahn's contention "difficult to interpret . . . It would appear that you think that the new Phillips note-purchase rights would provide that a person who acquires 30 percent or more of Phillips common stock would have the right to exchange his common stock for the . . . senior notes. This is not so.

"Only the Phillips shareholders who are not a 30 percent holder and not part of his group would have the right to exchange their common stock," Douce wrote.

That brought an angry response from Icahn, who said in a statement that he believed that all Phillips shareholders would be eligible for the $62 notes. "None of Phillips' published information disclosed that the rights would have any such flagrantly discriminatory provisions," he said.

Icahn said he is "considering ways to assure that shareholders are not precluded from receiving and acting upon Icahn's offer." He did not elaborate.

Icahn's dispute with Phillips has its origins in an agreement the company reached with Mesa Petroleum Co. Chairman T. Boone Pickens Jr. in December that ended an attempt by Pickens to take control of the company. Under that deal, Phillips proposed the complicated recapitalization plan that shareholders are to vote on Feb. 22, which the company said would be worth about $53 a share. Icahn and others on Wall Street who had invested in the company hoping to receive $60 a share from Pickens disputed the $53-a-share value claim.