CHICAGO (AP) _ A lawsuit accuses a company of charging up to $3,000 a year for a colon cancer drug that costs only $14.95 annually when used for treating sheep.

The lawsuit filed Tuesday in Cook County Circuit Court said New Brunswick, N.J.-based Johnson & Johnson charges ''an extortionate price'' for the drug levamisole.

Company spokesman Robert Kniffin said today he had not seen the lawsuit and could not comment extensively. But, he said, Johnson & Johnson believes the pricing of the drug is ''fair and responsible.''

Chicago lawyer Stewart M. Weltman filed the lawsuit on behalf of his client, Frank Glickman, who was prescribed the drug after colon cancer surgery in 1990. Weltman has asked the court to certify the lawsuit as a class action.

Wayne, N.J.-based American Cyanamid Co. sells levamisole for treating worms in sheep, but Johnson & Johnson sells the human version.

Johnson & Johnson's pricing of levamisole was criticized in a study released in May. Dr. Charles G. Moertel of the Mayo Clinic, who conducted the study, called the price difference ''unconscionable.''

Moertel said Johnson & Johnson charged $1,495 a year for the drug.

Levamisole is the only medicine that can prevent colon cancer from recurring after it is surgically removed. Colon and rectum cancer are the second-leading cause of cancer death in America, behind lung cancer.

Johnson & Johnson developed levamisole in the 1960s to treat worms in farm animals. The Food and Drug Administration in 1990 approved the drug for use in colon cancer patients.