WASHINGTON — Trauma surgeons at MedStar Washington Hospital Center didn’t know the name of the young man wheeled into the trauma center, unconscious and bleeding from his face and head after being hit by a car. Nor did they know he lacked insurance.

But as they worked to save his life, doctors and nurses at the capital’s largest hospital ran a dizzying battery of lab tests and high-tech scans. Surgeons operated repeatedly, at one point removing a portion of his skull to relieve pressure on the brain.

As happens daily in emergency rooms nationwide, the uninsured patient received medical care guaranteed by a generation-old federal mandate that requires hospitals to care for all in need, regardless of ability to pay.

For 26 years, the Emergency Medical Treatment and Active Labor Act, or EMTALA, has been a bedrock principle of American health care - passed by a bipartisan Congress, signed by a Republican president and largely unchallenged since by hospitals and doctors.

“Whether people know it or not, whether people appreciate it or not, access to emergency care became a right in this country in 1986,” said Dr. Wesley Fields, an emergency physician in Orange County, Calif. “But the law that did that never addressed the big question of whose responsibility it was to deal with the cost.”

That unresolved question - who pays? - helped shape President Barack Obama’s 2010 health care law and its requirement that Americans get health insurance. For years, it even convinced many Republicans, including former Massachusetts Gov. Mitt Romney, to champion an insurance mandate. But today, the insurance mandate is the central target of GOP opposition to the law.

Within days, the Supreme Court will rule on whether the new law is constitutional. If the law is upheld, millions of newly insured patients will have many of their hospital bills covered by insurance. But if the law, or just the insurance mandate, is struck down, those bills will be passed on to taxpayers, hospitals and privately insured patients, as they have been for the past quarter-century.

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The drive for a hospital mandate emerged in the 1980s out of outrage over stories like Sharon Ford’s.

Ford, who lived in a working-class suburb of Oakland, Calif., gave birth to a stillborn baby in 1985 after being turned away from two private hospitals that erroneously believed she lacked insurance. At one, she was refused admission even after a fetal monitor picked up signs that her baby’s heart was beating irregularly. By the time she made it to a public hospital, which scrambled to do an emergency caesarean section, the baby had died.

Ford’s case was not an isolated one. In Dallas, an 18-year-old man died from a severe infection after a local emergency room wouldn’t perform basic medical tests before sending him to the public hospital. In Chicago, one private hospital reportedly placed yellow stickers on the charts of patients without private insurance to avoid admitting them.

“We were seeing outrageous behavior on a daily basis,” said Dr. Steffie Woolhandler, a professor of public health at the City University of New York who helped document what was called “patient dumping.”

State leaders were the first to require hospitals to provide emergency care to all in need. But by the mid-1980s, pressure was mounting for a national solution.

Democrats who advocated universal health care, including the late Sen. Edward M. Kennedy of Massachusetts and Rep. Pete Stark of California, eagerly embraced a federal mandate on hospitals.

But the idea drew support from leading Republicans as well. “We cannot stand idly by and watch those Americans who lack the resources be shunted away from immediate and appropriate emergency care,” Sen. Dave Durenberger, R-Minn., the lead Senate sponsor of the mandate legislation, said at the time.

Sen. Robert Dole of Kansas, the majority leader and future GOP presidential nominee, said hospitals had an obligation to provide care. “We should expect nothing less,” he said.

The emergency treatment act, which threatens hospitals with the loss of federal Medicare funding, was ultimately included in a massive budget compromise signed by President Ronald Reagan in 1986.

Over the years, hospitals and federal regulators in Democratic and Republican administrations would tangle over how much care hospitals had to provide. But there would never be a serious challenge to the act’s legality or a move to repeal it.

The law requires emergency rooms to evaluate patients and stabilize those in need of urgent care. It does not compel hospitals to admit everyone for ongoing treatment.

There is broad agreement that the law put an end to the worst abuses. “It changed the way many institutions operated,” said Elvia Foulke, a former hospital executive at Citrus Valley Medical Center, a safety net hospital east of Los Angeles.

At MedStar Washington Hospital Center, a sprawling medical campus three miles from the U.S. Capitol, the emergency department sees its daily share of uninsured patients seeking care for everything from heart attacks to insect bites. Last month, more than 400 of 8,400 seen lacked coverage, according to hospital figures. Nationwide, the uninsured account for nearly a fifth of emergency department visits.

In nearly every case at MedStar, doctors and nurses never know who pays the bills. “It doesn’t enter the equation,” said the hospital’s emergency chief, Dr. Bill Frohna.

But the bills come due. And although emergency care accounts for a small fraction of total health care spending, many hospitals are feeling increasingly strained by the free care they provide.

Last year, MedStar Washington reported delivering $107.2 million in care for which it was not reimbursed. Nationwide, the total amount of uncompensated care provided to the uninsured reached an estimated $56 billion in 2008, according to one study.

Those costs have prompted financially strapped hospitals to rely on a complex system of shifting costs. Most of the burden falls on taxpayers, with the government providing tens of billions of dollars annually to help hospitals care for the uninsured. Privately insured Americans also pay a price as insurers raise premiums to reflect higher charges from hospitals.

In the past, the cost shifting was cited by many conservatives as a reason why the federal government should require Americans to have health insurance.

“If a man is struck down by a heart attack in the street, Americans will care for him whether or not he has insurance,” the Heritage Foundation’s Stuart Butler said in 1989. “We will not deny him services - even if that means more prudent citizens end up paying the tab.” Butler, like many Republicans, has since renounced the insurance mandate.