LONDON — Hospital doctors in England staged their first strike in four decades on Tuesday, disrupting treatment for thousands of patients in the National Health Service and escalating political tensions over a publicly funded health care system so revered that it was once likened to a national religion.

Operations were postponed and appointments canceled in a bitter dispute over pay and working hours between employers and junior doctors, a term that covers medical professionals with as much as a decade of experience.

With the junior doctors offering only emergency care, about 3,500 operations had been affected by Tuesday afternoon, including routine procedures for knee and hip replacements — prompting a warning from Prime Minister David Cameron that the labor action would create “real difficulties for patients, and potentially worse.”

Yet the dispute over the health system carries risks for the government. The National Health Service, which is funded by taxes and payroll deductions but has faced years of financial strain, delivers most treatment without charge. Despite regular funding crises, there has been no similar strike since 1975.

Read Also: Junior Doctors in UK to go on strike