For more than a year, National Medical Care Inc. has been fighting proposed federal cost-cutting regulations that threaten its position as the leading private provider of dialysis treatments for victims of kidney disease.

Although the verdict is still out, the private dialysis clinics, led by NMC, have won a White House review of the issue. Craig L. Fuller, presidential assistant for Cabinet administration, said the proposed regulations by the Department of Health and Human Services are likely to be considered by a cabinet committee soon.

The Boston-based NMC gets the "lion's share" of its revenues--about 74 percent in 1981--from its dialysis clinic business. Patients with kidney failure undergo dialysis treatment to remove toxic wastes and other life-threatening impurities from their blood.

The federal Medicare program pays 80 percent of treatment costs for most kidney patients, spending $1.8 billion on dialysis treatment for 59,200 patients. NMC has about 17 percent of the "market" for dialysis treatments, competing with other private clinics, hospitals, and with equipment used in home treatment. In 1981, NMC treated more than 11,000 patients, reporting net assets of $254 million and net income of $19.7 million.

Troubles began on July 31, 1981, when Congress ordered the Department of Health and Human Services to control costs for the Medicare dialysis program.

Last February, HHS proposed decreasing the amounts that both clinics and hospitals could charge for dialysis treatments, with clinics bearing the larger cutback.

Former HHS secretary Richard S. Schweiker strongly favored the proposals, because they permit more "efficient" dialysis treatment, encouraging less-expensive home dialysis, while still providing a "good rate of return" for the private treatment centers, according to an HHS spokesman.

Dr. Constantine L. Hampers, president and chief executive of NMC, has argued that the proposals would discriminate against clinics, which on average charge less than hospitals for dialysis treatments. And he warned that NMC would have to close 60 of its 160 kidney dialysis clinics if the cuts went through.

On Wall Street, NMC's stock, plummeted from 25 7/8 in April 1981 to 5 1/4 by July 1982. Earnings per share fell from a $1.40 in 1980 to $1.09 in 1981. Many analysts put NMC on their hold list, and company expansion was "throttled back," in the words of Harry E. Wells, director of research at Adams, Harkness & Hill Inc. in Boston.

Hampers and the private clinics began to fight back. Letters of protest from dialysis patients began pouring into Washington, and congressional hearings were held. Some influential political figures lined up against the proposed regulations, including then-representative Margaret Heckler (R-Mass.), who wrote Schweicker on July 21, 1982, that she believed the pending changes were "ill-advised."

The cost reimbursement HHS proposed would discourage dialysis service by clinics and hositals, she said. "While I understand the necessity to cut the rising cost of federal health programs, I believe that the pending regulations are ill-advised, in terms of the suffering to kidney disease patients they would cause."

Schweicker sent a dialysis fee proposal to the White House for approval the week before he announced his resignation. But the National Journal reported the proposal "has reportedly been labeled too controversial to proceed with at this time."

Heckler was nominated to replace Schweicker and suddenly, instead of confronting a hostile secretary of HHS on the issue, the private dialysis lobby had the new secretary-designate as a powerful ally.

A revised set of regulations went to the White House for review last month, and reportedly close most of the gap between fees paid to hospitals and clinics--although the new fee levels are still too low to suit the clinics, officials said.

Fuller said there is likely to be a Cabinet committee meeting on the dialysis treatment proposals this month. No decision has been made.

Meanwhile, NMC's stock began to move rapidly upward--aided by the general recovery of the stock market, and perhaps because investors' fears of damaging government regulations had eased, said James R. Latham, health care analyst for Interstate Securities Inc. in Charlotte, N.C.

In addition, Hampers has begun to talk again about a brighter future for NMC, after nearly a year of grim predictions.

For whatever reasons, NMC's stock jumped several points to 13 3/4 the first week of February and has since inched above 16.

Analysts hold differing opinions about NMC's prospects. Wells, of Adams, Harkness & Hill, said he is recommending a hold on the stock until after he sees NMC's success at diversifying.

Latham, of Interstate Securities, said the company's long-range future looks good, in part because of the network of clinics and its track record of providing low-cost services. And he likes the "aggressiveness" of NMC's management--displayed in the year-long fight over the government regulations.