If you've been reading a newspaper or watching cable TV, you probably have the impression that President Obama passed his 100th day in office sometime in mid-April and that this event carried great significance or legal importance.

You would get this impression from the way the news media jumped the gun with intense coverage of this imaginary watershed. For the record: April 29 is the 100th day of the new presidency. For those who might care, we should add that Obama will not actually complete 100 days in office until 1 p.m. on April 30, which would be 2,400 hours after he took the oath of office at noon on Jan. 20 (note one hour of adjustment for Daylight Saving Time).

What difference does any of this make? None, really. Unless you happen to be in the news business, or the business of getting your point of view into the news. For all who are part of this constant conversation, the 100-days milestone has been a preoccupation for weeks. No one waits for the calendar on these things, as that would allow our competitors in reporting and advocating to steal a march on us. To be behind the news curve is worse than death.

As a result, this traditional occasion for taking an early analytical look at a nascent presidency comes earlier and earlier, and what would have been a preliminary judgment at best becomes less meaningful than ever.

Truth be told, the 100th day has no significance whatever in terms of the Constitution, the executive calendar or the congressional calendar. It means not a thing to any legal or legislative process. Yet that has never restrained those who see a purpose in sizing up each new president after a few months in office, using the poetic interval of 100 days (much as Abraham Lincoln spoke of "four score and seven years" and not "eighty-seven").

Even the White House has given up and joined the parade. After calling it a "Hallmark holiday" akin to Grandparents Day or Secretaries Week, the Obama team scrambled to mount a "100 days town hall meeting" and a prime-time news conference to mark the date.

The previous reluctance might have reflected some uneasiness in the White House about the tone and tenor of all the appraisals being made. But now that the returns are in, and generally positive, the president's team is eager to tout them.

It turns out to be a good time to strike up the band, if only because a spate of polls shows the president to be cruising up around 70 percent approval in the personal category and winning a solid majority for his program as well.

The 100-day assessment is generally attributed to the early achievements of Franklin D. Roosevelt's presidency, from March of 1933 (Inauguration Day was later then) through mid-June. Roosevelt used a "bank holiday" (spin talk for "temporary bank closings") to quell the panic runs and usher in an era of federal regulation. He also launched many new programs he hoped might stimulate economic activity and put people back to work. Congress, heavily Democratic and thoroughly frightened, gave FDR pretty much everything he asked for in record time.

There has not been a comparable period of achievement for a new president since, although President Ronald Reagan was able to cut taxes and reprioritize defense in the early months of 1981, aided again by a cowed Congress and a national mood of readiness for change.

But the current 100-day frenzy may have less to do with real history than with the current needs of contemporary news organizations. Given a media environment in which urgent dispatches detail the romps of a new White House dog, it's no surprise that even an artificial mini-milestone causes palpitations.

The daily fascination with all things Barack Obama absorbs the cable TV news competitors like no other subject. Even the peregrinations of the Dow and a steady stream of horrific crimes are not as constant a source of material.

That is in large part because the Obama phenomenon made the last presidential cycle the best-watched election in history. News organizations old and new saw tremendous audience interest in the Obama story and capitalized on it.

It was, and it remains, the one ray of hope for many in an industry mired deep in an advertising recession. Some of journalism's grand institutions teeter on the brink of bankruptcy, while insouciant online outlets are still struggling to convert their popularity and promise into cash.

So yes, the news media obsession with Obama has to do with the fate of the nation in parlous times; but it is also about the survival of the news business itself in a season of mortal peril.

I was taking pictures alongside other tourists at the Temple of Karnak in Egypt earlier this month when a member of the national police marched across 50 yards of sun-blasted terrace to talk to me. He was wearing the black uniform and beret of the security forces, and he had an assault rifle strapped acoss his chest.

"Where from?" he asked me.

"America," I said.

"Obama!" he shouted, suddenly beaming and nodding.

It might have been startling, except that something similar happened every day of the dozen I was there.

It's a commonplace that President Obama has altered the perception of the United States around the world. But meeting people in an Arabic-speaking country brings that statement to life in compelling ways.

Shopkeepers and cabbies, students and business people, young and old are eager to signal their interest and approval. America, an old and well-known actor on the world stage, has undergone a character transformation overnight.

As one American woman said to me: "I don't have to pretend to be Canadian any more."

It is impossible to escape the sense of something opening all around you. If it is not a new era, it is at least a new window of possibilities. Perhaps the "clash of civilizations" paradigm that dominated after Sept. 11 will not prevail indefinitely.

Yet, alongside that glimpse of hope there are shadows of caveat and doubt. For one thing, the impressions Americans receive in foreign countries are often formed inside a tourism bubble, where people have a strong interest in courting our friendship.

Beyond that, the sheer intensity of the Obama phenomenon suggests impermanence. Having dazzled his way from London to Istanbul to Baghdad, the American president is a starburst over the global consciousness -- much as he was on the U.S. political scene late in 2007. He maintained altitude well enough in 2008 to be elected, and he remains popular after three months in office. But staying aloft this well as a world figure will be more difficult.

The international version of the Obama Moment is unlikely to survive the first international crisis in which the Obama administration must defend the U.S. interest. And sooner or later, that crisis and choice will come, forced by the complexities of world problems and the simplicities of domestic politics.

For now, the Obama administration is doing all it can to postpone the day of reckoning. The White House maintains that the national interest can be redefined to harmonize with the global good. It's an inspiring vision, but it contends with powerful impulses deep in our political nature.

In an era of economic distress, it is natural for our country and all countries to put blame on foreign competitors and to fear international exposure. And in the age of terrorism, it is natural for any people to insist on having every weapon available to protect themselves.

The Obama administration is asking us to transcend these basic instincts. On the economic front, it argues that a retreat from trade would deepen the recession for everyone, as it did in the 1930s. On the security front, the president says we must not use torture as a means of interrogation -- even if we believe it might expose a plot or a terrorist in the short term. To do so, he says, suborns the principles the nation was founded to uphold while yielding comparatively little of value.

That view has been vigorously challenged by conservatives, chief among them former Vice President Dick Cheney, who is closely associated with the aggressive techniques. The argument is that in a brutal world, we must have all potential tools and weapons available.

As the debate goes forward, experts will disagree about the usefulness of waterboarding and other means most regard as torture (or tantamount to it). Cheney and others argue the extreme methods bore fruit, and they say classified information would prove it.

Ultimately, the Obama case rests on the idea that Americans are safest in a world where people see the United States as a beacon of principle and hope. Whatever dividends torture may yield must come at enormous cost.

Attorney General Eric Holder says the U.S. can "reclaim its standing in the world" only by making a clean break with torturous techniques. That view is popular in public opinion polls, at least in part because of the lingering unpopularity of the last administration.

But the old anger and resentment may fade with time. And the Obama White House can chart its new course toward world approval only so long as no new terrorist attack strikes the homeland. If one does, Cheney's attitude will be back with a vengeance.