WASHINGTON — The Trump administration proposed on Monday to cut costs for Medicare by reducing the number of prescription drugs that must be made available to people with cancer, AIDS, depression, schizophrenia and certain other conditions.

Under the proposal, health insurance plans that provide drug coverage to Medicare beneficiaries would no longer have to cover all of the drugs in six “protected classes.”

The change would take effect in 2020 and would lead to lower out-of-pocket costs for Medicare beneficiaries, the administration said.

The proposal comes six months after President Trump vowed to “bring soaring drug prices back down to earth” — and three weeks after many Democrats swept to victory in midterm elections by promising to rein in drug prices.