Diabetes and its complications cost the nation some $20.4 billion last year, with about $10.8 billion resulting from lost productivity and the rest from medical bills, says a study released Saturday.

Direct health care costs included $6.9 billion for inpatient hospital care, $1.7 billion for outpatient care such as doctor visits and medications, and $942 million for nursing home care.The disease, its complications and related issues accounted for more than 11.5 million days in the hospital, said the report by Pracon Inc., a research and consulting firm in Reston, Va.

It was presented at the American Diabetes Association's annual scientific meeting in New Orleans.

In all, the report estimated, 6.5 million Americans had diagnosed cases of diabetes in 1987. Other studies have shown that about 5 million more Americans have the disease but do not know it.

The study estimated that nearly 565,000 new cases of diabetes were diagnosed last year, and that the disease contributed to an estimated 201,000 deaths.