If present trends in U.S. health care continue, you could be denied medical treatment precisely when you need it most--when you are elderly and ailing.

This startling conclusion goes directly contrary to widespread assumptions about our elaborate system of health care delivery, and to official statements concerning the ready availability of medical services under Medicare, Medicaid, and other programs. Yet it is clearly supported by the record on medical regulation in recent years. It also tracks closely with what has happened under government-managed health care systems in other countries.

For the better part of a decade, federal regulators have been working diligently to reduce the level of benefits provided to Medicare recipients, as well as to other beneficiaries of government-assisted medicine.

Principal reason for this effort to cut back on the amount of care delivered is official concern about the spiraling costs of Medicare and other government health programs, and of health care expenses generally. Under prevailing systems of "third party" payment, demand for services, and resulting costs, have skyrocketed. Health care regulators are trying to slow this trend by pressuring for cutbacks, including levels of hospital admissions and days of care provided.

Official documents of the U.S. government promise elderly Americans extensive days of free--or tax-supported--care. The official Medicare Handbook of the Department of Health and Human Services says, for instance, that Medicare patients are entitled to 60 days in the hospital per benefit period, after a deductible, plus an additional 30 days with a co-payment. Moreover, "after you have been in the hospital 90 days, you can use all or some of...60 reserve days if you wish. "

To most people, that sounds as if you are entitled to up to 150 days of tax-supported care, courtesy of the federal government. But if you wind up in the hospital as a Medicare patient, you're apt to discover that this verbiage doesn't mean much--since hospitals and physicians are under constant pressure to move you out as soon as possible.

What the Medicare Handbook manages to obscure is that while you may be entitled to up to 150 days of care according to the law, Uncle Sam won't actually pay for it. The financial burden for this alleged guarantee, instead, is fobbed off on the hospital and attending physician--who therefore have powerful incentives to get you quickly through the system.

Take a look at what Medicare actually pays for, and you discover the average reimbursement to hospitals in 1989 came to 4.7 days of care (exactly half of what was billed). Even for the most complex and costly procedures, involving life-threatening conditions, Medicare will reimburse, on average, for 10 or 12 days of care (again, approximately half of what the hospitals bill).

Looking even less like 150 days of tax-supported care are federal documents advertising a decline in the number of per capita hospital admissions and average length of stay under recent regulations. For the elderly, admission rates fell by 16% from 1983-87, while average length of stay was reduced from 10.37 days to 8.71 in the decade of the '80s. These reductions stem from the Prospective Payment System (PPS), adopted by the federal government in 1983.

The regulators view these declining days of care and rates of admission as signs of progress in the battle against cost. Dr. Gail Wilensky, formerly head of the Federal Health Care Financing Administration (HCFA), reported last year that, under PPS, "the average length of stay for Medicare patients in short-stay hospitals decreased from 10.0 days in fiscal year 1983 to 8.5 days for PPS hospitals in fiscal year 1989...Total Medicare inpatient admissions also fell from 11.7 million in fiscal year 1983 to 10.4 million in fiscal year 1989. "

Prospective payment reverses the incentives that existed under previous billing methods--in which providers were reimbursed according to their costs or customary charges. …