Barrie Dowdeswell, general manager of the Royal Victoria Infirmary here, stands at the front line of Britain's troubled National Health Service, once viewed as a world model of a successful national medical service.

He explains that his staff of 3,500 is often fighting a losing battle against increased demand, essentially rationing health care for lack of funds.

At the hospital, the average waiting time for a patient seeking a cataract operation, for example, has doubled to more than a year.

Six times this year, surgery to repair aneurysms _ a potentially life-threatening condition to the arteries _ has been postponed at the last minute because of a scarcity of skilled nurses.

Kidney dialysis patients and bone-marrow transplants are also strictly limited.

"The cash squeeze has driven down the number of patients we can take in," Dowdeswell said. "And it's really hitting us this year."

The problems at the Royal Victoria Infirmary are typical of those found throughout the National Health Service today.

The NHS, by all accounts, is in a state of crisis. More than 660,000 people are on waiting lists for elective surgery nationwide. Nurses, poorly paid by international standards, are seeking jobs in other countries or in other fields, quitting at the rate of roughly 30,000 a year.

Many buildings are old and run-down. Budget restraints forced hospitals to drop 3,500 acute-care beds last year. Earlier this year, the Association of Community Health Councils of England and Wales, a consumer lobbying group, warned, "Unless there is action now, some parts of the NHS already on the brink of collapse will simply fall apart during 1988."

Founded 40 years ago as the first comprehensive health-care service in history, the NHS promised to provide every citizen with equal access to "whatever medical treatment he requires, in whatever form he requires," according to the economist Lord Beveridge, the system's principal architect. But that pledge is threatened.

There is sharp disagreement between health professionals and the Conservative government of Margaret Thatcher about the root cause of Britain's health-service crisis.

Health workers and lobbying groups insist the system is simply overburdened and underfunded. "The NHS is being systematically starved of the resources it needs," Dr. John Harvard, secretary of the British Medical Association, said, echoing a common sentiment.

For its part, the government replies that much of the problem is poor management and a lack of market incentives in a sprawling public-sector monopoly.

The NHS issue has recently been pushed to the center of the British political stage. London newspapers have run front-page stories on the most heart-rending waiting-list cases, notably small children seeking vital heart surgery.

Last February, tens of thousands of British nurses went on strike. Shortly afterward, Thatcher announced a sweeping government review of the NHS, due to be completed this fall and headed personally by the prime minister.

Thatcher has pledged to "reform" the service, a task widely regarded as the stiffest challenge her government has faced since the coal strike of 1984-85.

Many of the problems confronting the service, to be sure, are difficulties shared by the health systems of most developed nations, particularly the soaring costs of high-technology medicine and an aging population.

Still, the fashioning of Britain's new policy is being closely watched internationally because it was the pioneer of national health care and is the largest and most centralized of Europe's public health-care systems. With about 1 million workers, it is Western Europe's biggest employer. It treats 30 million patients a year and has an annual budget of $37 billion.

For Americans, the challenges facing Britain's national health service are instructive because the Democratic presidential candidate, Gov. Michael S. Dukakis, has stated that, if elected, he will strive to establish a national health-care system in the United States.