Sahara Chhabra, Texas, US

A We're neither economic forecasters nor political prognosticators by trade.

But you don't need to be either to see that, right now, the United States certainly holds a robust lead in the race for hegemony.

The US economy is about five times as large as China's and nearly 15 times larger than India's, yet it has about a quarter of the population of either of those nations. That can only give the US a real advantage in providing education, health care and national security, plus all the other stuff that makes a country thrive.

But "right now" doesn't mean forever. All you need is a ruler to draw the straightline extrapolation that shows China and India, with their faster growth rates, catching up to the US in economic size. For China, that would occur as early as 2045, and for India, the date would be some 20 years later. This is why you so often hear experts predicting that by mid-century, the US will be trailing the two new world superpowers.

We'd say, not so fast.

Straight-line calculations about the US, China and India are just that. They assume that all three countries will enjoy smooth upward rides: no recessions, no banking breakdowns, no political crises, no disruptive social uprisings. Unlikely?

For sure.

With China's massive experiment combining communism and capitalism, India's entrenched bureaucracy and corruption, and America's long-term entitlement obligations, it is far more probable that growth trajectories will zig and zag more than zoom.

Further, straight-line calculations do not take into account relationships with other parts of the world, such as the Middle East, where ties and friendships with one country or another could very well change over the next few decades.

Given that, then, what broad-brush scenario would you bet on for the next 50 years? Would it be America's 3% annual growth or China and India at 8%? We'd take America for a simple yet incontrovertible reason. Its system . . . the sum of all its parts . . . works. And when it breaks, it bounces back fast.

Don't worry, we're not going to start singing the 'Star Spangled Banner'. We just believe US economic dominance isn't a function of how long it has been leading the pack. It's about how America operates as a country. We're talking, mainly, about freedom and stability.

US political parties disagree, often vehemently, but the government never stops running. Generally speaking, the US justice system is fair. Health care, while inconsistent in delivery, is widely available. And even though secondary education in America gets roundly knocked, it has without doubt the best system of higher education in the world, turning out the world's most skilled, innovative science and engineering Ph Ds.

The US has a final competitive advantage that is as powerful as it is unique:

its confluence of bright, hungry entrepreneurs and flush, eager investors. Yes, China and India have ambitious people who dream of building their own companies, and, increasingly, are getting the chance. (The US venture firm Kleiner Perkins Caufield & Byers, for instance, just opened offices in Shanghai and Beijing. ) But neither China nor India comes close to the US in terms of this 'killer app', and it will take years of venture capital flowing in before the Chinese finally let go of their rote approach to work and embrace innovation with true entrepreneurial spirit.

China has other challenges as well. Aside from its risky social experiment, it has an economy in which fewer than a quarter of its people truly participate. Its one-child policy is exacerbating the problem of its rapidly aging population. India, meanwhile, will continue to struggle with its overwhelming number of have-nots and its aforementioned corruption problem. True, India is a democracy, but a democracy muddled by a profusion of divergent political parties.

Now, we're not saying the American system is perfect or its economy invulnerable.

If you get out your ruler and straight-line extrapolate again, you see a budget deficit that explodes over the next 20 years.How the US handles that problem with a combination of tax and spending policies will determine the strength of its growth engine. Fortunately, America's stable, highly adaptable system has conquered enough major problems . . . from the Depression to the Cold War . . .that there is more reason for optimism than despair.

In the end, we'd make the case that American economic leadership will be with us for most, if not all, of the century. It will by no means "rule, " as it did at the turn of the century. But it will remain ahead until other nations develop a total economic and social system that works as well. There's a lot more to the world's economic future than a straight-line extrapolation can tell you.

Jack and Suzy Welch are the authors of the international best-seller Winning. You can email them questions at Winning@nytimes. com.