The mail-order pharmacy business will continue to grow at a substantial rate, despite the adverse publicity from a criminal lawsuit filed by Latah County against a giant in the industry, a health care investment specialist said.

Last month, Latah County Prosecutor Craig Mosman filed an involuntary manslaughter charge against Medco Containment Serves of New Jersey in the death of 70-year-old Iris Hemmelman of Princeton, Idaho.Hemmelman died Jan. 28 after taking an allegedly mislabeled prescription she received from National Prescription Services of Las Vegas, a Medco subsidiary. An autopsy showed a toxic level of coumadin, a blooding-thinning agent. She was prescribed medication for water retention.

"The economics are too powerful for anything but high growth in the mail-order pharmacy business," said David Saks, president of Saks Health Care Investments Advisers at River Vale, N.J. "This charge is a mere red light on a major highway of high growth."

But Stephen Amitay of Washington, D.C., said the criminal lawsuit is catching the attention of national lawmakers.

"We're monitoring the situation because this is a pretty big case for the mail-order industry," said Amitay, a staff member for a subcommittee of the Senate Committee on Governmental Affairs that conducted hearings on Medco Containment Services in the summer of 1987.

"If we can get the big insurance companies to stop looking at bottom lines and start looking at safety rec-ords because of this, then it will be a lot better for everybody," he said.

Hemmelman's husband, Wayne, is an electrician at Washington State University and received medicine from National Prescription Services through his Blue Cross coverage.