District Attorney Ira Reiner, citing a "strong possibility" that unpasteurized milk was deliberately used in tainted Mexican-style cheese, announced a criminal probe yesterday of a bacterial outbreak suspected of killing 51 people since mid-March.

A search warrant citing suspicions of involuntary manslaughter and of several other crimes was used to seize records at Jalisco Mexican Products Inc. late Tuesday, authorities said.

In a statement, Jalisco president Gary McPherson said: "If in fact we are being accused of any criminal intent, we absolutely deny these charges. We will be making an internal investigation as to why these accusations could have been made." He said he was dismayed that a warrant was issued "when I have made all our records available since Day One."

Reiner said records showed that the Jalisco plant in Artesia received about 10 percent more unpasteurized milk a month than was pasteurized for its final product, indicating that unpasteurized milk somehow was mixed into the cheese.

He said investigators found during the weekend that the plant's pasteurization equipment was working properly and that unpasteurized milk could not have been introduced into the cheese inadvertently. "It raises the strong possibility that it was put there deliberately," Reiner said.