The possible mistreatment of research animals at the University of California, Riverside, could jeopardize millions of dollars in federal grants, officials of the National Institutes of Health said. Allegations of mistreatment filed by animal rights activists after an April break-in at UC Riverside laboratories are being investigated by the health institutes to see if laboratory guidelines were violated. Violation of those guidelines can result in the loss of federal grants for animal research as well as financing by the U.S. Health and Human Services Department. Health institutes officials would not comment on the status of the investigation. The amount of federal grant money used for animal research at UC Riverside was not immediately known.