During a surprise visit last month, state investigators witnessed a worker in the Beth Israel Deaconess Medical Center nursery sloppily cleaning a board that had been used during a minor surgery, contaminating a nearby counter.

They also discovered during the inspection that nurses treating the tiniest of babies had received no special training in how to transfuse blood into their delicate veins.

And they watched as a doctor used medical instruments to examine the eyes and ears of one infant - and, then, a half-hour later, used the same ones on a second baby without disinfecting them.

These and other safety lapses, made public yesterday, turned up during an investigation prompted by a cluster of hard-to-treat bacterial infections among mothers and their new borns who had been at the Harvard-affiliated hospital since late last year.

The state investigation didn't establish a direct link between the deficiencies and the infections, but its findings open a window into the inner workings of an institution that has undertaken an unusually public campaign to eliminate hospital-acquired infections and other preventable errors. And it reveals that, despite the best of intentions, reducing mistakes is a formidable challenge.

"The hospital has to fix this," said Paul Dreyer, director of the state's Bureau of Health Care Safety and Quality, whose staff conducted the investigation. "There are systemic problems, there are breaks in practice, there is an ongoing cluster of cases that's not been resolved."

At the same time the state provided the Globe its thick report late yesterday afternoon, Beth Israel Deaconess released an even bulkier response, detailing how it intends to better protect patients from harm. In a lengthy interview, a top hospital administrator conceded that the investigators from the state Department of Public Health had revealed significant shortcomings in safety procedures on the obstetrics and newborn wards.

Dr. Kenneth Sands, senior vice president of health care quality at the sprawling Longwood area hospital, said it has moved swiftly to correct problems identified in the inspection and will require all doctors, nurses, and other healthcare workers to complete compulsory lessons on infection control by May 1.

"We've always known that it's extraordinarily difficult to set ourselves on a path to have no preventable harm" to patients, Sands said. The lapses cited by the state, he said, "are unacceptable, and we fully agree that . . . they need to be corrected." He pointed out that the hospital had succeeded in reducing some of the most worrisome hospital infections.