Many health maintenance organizations are pulling back in their efforts to sign up Medicare beneficiaries, finding it difficult to turn a profit on these patients. Yet Washington continues to push HMOs as a means of controlling Medicare costs.

Here are a few of the economic realities:

• The average cost to Medicare for treating 90 percent of beneficiaries in 1996 was $1,200.

• But for the sickest 10 percent, the cost averaged around $37,000.

• Only 15.6 percent of Medicare's 37.5 million members are enrolled in Medicare HMOs nationwide.

• Coverage varies widely, ranging from 39 percent of Medicare beneficiaries in California enrolled in HMOs to none in South Carolina.

Though the government contends it has overpaid Medicare HMOs, the companies say the federal monthly stipend for each enrollee is not enough to provide extensive benefits and a number of them have cut services. This is especially the case in rural areas, where Medicare HMOs cannot enroll enough members to negotiate discounts with local health-care providers.

As a result, analysts say, HMOs must focus primarily on urban markets and avoid offering generous prescription drug plans, which can attract a disproportionate number of sick people.

According to the Health Care Financing Administration, which runs Medicare, managed-care companies receive some $5,688 annually on average for each of their Medicare patients.