People who take four or more drinks a day or smoke a pack or more of cigarettes or overeat are filling more hospital beds and accounting for even more of the huge national health bill than even doctors have realized.

They are placed in the same class -- though they tend to be even sicker -- than people who use street drugs or who refuse to follow doctors' orders in a serious illness.

Two Harvard researchers, studying the patients of six representative hospitals, have found that in a year's time such persons were at least 50 percent more likely than other patients to land in the hospital, and probably be there repeatedly.

Twenty percent died in the hospital or were terminally ill, compared with 3 to 4 percent of other patients.

Drs. Christopher Zook and Francis D. Moore -- noted Peter Bent Brigham Hospital surgeon -- report in today's New England Journal of Medicine that, for many reasons, just 13 percent of all patients ran up half of the total hospital expenses for the year of 1976.

Forty percent of these patients running up bills of $5,000 or $10,000 or more were over 65. This was no surprise, the researchers say. But "an unexpected finding" was the long and frequent hospitalization of five groups: Those who drank more than four "hard drinks" (such as whiskey or gin) daily, those who smoked a pack or more daily, the obese, users of heroin or other "hard drugs," and those who persistently ignored doctors' advice.

Smokers typically had lung or blood vessel diseases; alcoholics, liver or nerve diseases; the obese, heart disease or diabetes.

Over five years, such persons made up 35 percent of the higher-cost patients and only 20 percent of low-cost patients in one hospital. In a larger referral hospital, those with the poor health habits made up 73 percent of the high-cost and only 45 percent of lower-cost patients.