WASHINGTON — Thousands of Medicare patients with severe chronic illnesses such as Alzheimer’s would get continuing access to rehab and other services under a change agreed to by the Obama administration, advocates said today.

The proposed agreement in a national class action suit would allow Medicare patients to keep receiving physical and occupational therapy and other skilled services at home or in a nursing home so they can remain stable, said Gill Deford, a lawyer with the Center for Medicare Advocacy.

That’s been a problem for some because of a longstanding Medicare policy that says patients must show improvement to keep getting rehab.