Doctor errors led to as many as one-quarter of the deaths of patients being treated for heart ailments, strokes and pneumonia in 12 hospitals studied by Rand Corp. researchers.

Doctors improperly treated patients complaining of chest pains, prescribed the wrong kind of antibiotics for pneumonia and misdiagnosed strokes, said a report on the study in Saturday's edition of The Annals of Internal Medicine.The researchers cautioned that the findings are preliminary and warned against generalizing the results over the nation's hospitals. It also said the doctor errors were common and relatively easy to correct.

"A hospital's quality assurance committee should approach these findings with a certain sense of optimism," the report said. "Although these probably preventable deaths occurred with what we consider surprising frequency, they were due to a small number of . . . causes."

All three of the physician panelists who reviewed the records of the 12 hospitals agreed that 14 percent of the deaths probably should have been prevented. Two out of the three agreed that 27 percent of the deaths were probably preventable.

Dr. Robert W. Dubois, who headed the study, said hospital patients should not be alarmed.

"The overwhelming majority - over 95 percent - of the people admitted to a hospital don't die. This is a non-issue for them," he said. "So it's important to put this in perspective."

The study by the Santa Monica-based Rand Corp. was based on a review of 182 patients who died in 1985 at hospitals owned by American Medical International of Beverly Hills, a chain of 115 hospitals in the United States and abroad.