An unpublished Veterans Administration report indicates that the Reagan administration's budget proposal for fiscal 1989 would cause a reduction in the agency's medical services, according to Sen. Alan Cranston, D-Calif.

Cranston, chairman of the Senate Veterans Affairs committee, said the administration withheld vital information about the prospective shortfall when VA officials testified to Congress on the agency's budget. He plans to hold a hearing on the report, which he said he received unofficially.He said the VA report shows that the administration's budget proposal of $10.32 billion for the agency would fall $819 million short of what VA hospitals need to avoid cutbacks.

Actually, Cranston said, the shortfall may be closer to $604 million because Congress last month appropriated $10.5 billion for the Veterans Administration, about $215 million more than requested by the president.

The agency report, according to Cranston, said the cost-cutting options facing the VA include: closing some medical centers, reducing inpatient admissions, laying off hospital employees, shutting down a number of Vietnam veteran counseling centers, eliminating VA kidney transplants and certain forms of dialysis care, restricting other organ transplants, eliminating or greatly reducing the dispensing of drugs and cutting back sharply on nursing home care.