President Lyndon B. Johnson uses the last of many pens to complete the signing of the Medicare Bill into law July 30, 1965, at ceremonies at the Truman Library in Independence, Mo., with former President Harry S. Truman at his side.

Washington ? Rarely does the government, that big, clumsy, poorly regarded oaf, pull off anything short of war that touches all lives with one act, one stroke of a president’s pen. Such a moment now seems near.

After a year of riotous argument, decades of failure and a century of spoiled hopes, the United States is reaching for a system of medical care that extends coverage to nearly all citizens. The change that’s coming, if today’s tussle in the House goes President Barack Obama’s way, would reshape a sixth of the economy and shatter the status quo.

To the ardent liberal, Obama’s health care plan is a shadow of what should have been, sapped by dispiriting downsizing and trade-offs.

To the loud foe on the right, it is a dreadful expansion of the nanny state.

To history, it is likely to be judged alongside the boldest acts of presidents and Congress in the pantheon of domestic affairs. Think of the guaranteed federal pensions of Social Security, socialized medicine for the old and poor, the civil rights remedies to inequality.

Only once before

Change is coming, it now appears, but in steps, not overnight. The major expansion of coverage to 30 million people — powered by subsidies, employer obligations, a mandate for most Americans to carry insurance, new places to buy it and rules barring insurance companies from turning sick people away — is four years out.

In contrast, on June 30, 1966, after a titanic struggle capped by the bill signing a year earlier, President Lyndon Johnson launched government health insurance for the elderly with three simple words, as if flicking a switch: “Medicare begins tomorrow.”

Obama practically needs a spreadsheet to tell people what’s going on and when.

Yet if the overhaul goes through, he and LBJ will share a distinction: the only two presidents to succeed with a transcendent health care law.

You can be sure Obama, a student of history, is aware of how LBJ captured the moment when Medicare became law with his pen. That happened in Independence, Mo., in the presence of the very first American to sign up for the program: Harry Truman. The ex-president had ended a world war but could not achieve national health insurance in his time.

“Care for the sick, serenity for the fearful,” Johnson promised that day. “In this town, and a thousand other towns like it, there are men and women in pain who will now find ease.”

Said Truman: “I am glad to have lived this long.”

Ted Kennedy lived long enough to see a goal of his lifetime take shape but not long enough for it to happen. His death last summer was almost the death of the whole plan because a Republican won his Senate seat, changed the voting balance and left despondent Democrats in search of a second wind, which they found.

‘Medical Soviets’

Why is this so hard? In part, because self-reliance and suspicion of a strong central government intruding into people’s lives are rooted in the founding of the republic, and still strong.

The colonial insurgents who dumped British tea into Boston harbor inspired the name and agitating spirit of today’s tea party protesters, who rolled a taped-together health care bill up the Capitol steps like toilet paper to show their disdain. “Grandma’s not Shovel-Ready,” said one of their signs last week, playing off a fear the aged will see their care rationed away.

In 1854, President Franklin Pierce vetoed a national mental health bill on the basis that it would be unconstitutional to treat health as anything but a private matter that is none of the government’s business.

In 1929, the American Medical Association denounced proposals for organized medical services as an “incitement to revolution” at the hands of “Medical Soviets.”

And that wasn’t even about government-run health care. The AMA’s fierce opposition to collectivism included objections to private health insurance, the norm today, and the pooling of doctors into what became health maintenance organizations decades later.