The operation of 75 care homes is at "significant risk" as they have a "status red" rating due to staffing problems amid the coronavirus crisis.
Care homes, particularly those for the elderly, are at the frontline of the fight against Covid-19, with a large proportion of deaths occurring among vulnerable residents in private and public facilities.
It emerged at the weekend that 21 people had died in one care home alone - St Mary's Hospital in the Phoenix Park.
Serious questions have been raised about the help given to nursing homes in the early days of the emergency.
Some nursing homes have also seen a staffing crisis as workers have either fallen ill with the virus or have had to self-isolate because they have been in contact with a suspected case.
The HSE last night defended its response as it revealed 75 care homes had been given a "red" rating in a traffic light system of assessing long-term residential care facilities in receipt of additional support.
There are 425 homes getting some level of help, ranging from infection control advice to extra staff and deliveries of personal protective equipment (PPE).
The HSE's chief operations officer Anne O'Connor said 221 of these were deemed stable after some intervention and had been categorised as "green".
Another 129 continued to need "significant enhanced supports".
Of those in the red, "at significant risk in terms of operation", 17 were HSE-run facilities. Ms O'Connor said the 75 homes were "particularly challenged" in terms of having enough staff.
She said 119 of the HSE's community staff and approximately 100 acute staff had been deployed by the HSE to care homes as "boots on the ground".
These deployments have been weighted toward the homes whose operations have been most at risk.
Ms O'Connor also warned that as coronavirus testing is ramped up in care homes there will inevitably be more outbreaks identified.
She said the challenge for the HSE was to identify the nursing homes "that have a critical need for a high level of support".
Ms O'Connor said nursing homes had been prioritised for deliveries of PPE and accounted for 60pc of supplies provided by the HSE in the past week.
She insisted the supply of PPE to nursing homes was "very, very significant".
HSE chief executive Paul Reid said the number of staff redeployed on its own didn't reflect the scale of the HSE's support for nursing homes in terms of resources.
He gave the example of a home in Louth that had been "practically taken over" by the HSE, and pointed to the support provided by multi-disciplinary teams of health professionals.
"If you were to calculate the total resource committed to private nursing homes it would be very significant," he said.
Mr Reid revealed the HSE planned to almost double its increased spend on PPE, and hoped that some of it could be provided by domestic suppliers.