The humble bar code, the rectangular thicket of slender bars and spaces on products, ignored by shoppers, indecipherable to humans, is joining the forced march of globalization.

For American retailers, whose checkout-line bar-code scanners will be expected to read the global bar-code standard by Jan. 1, the required changes in computer systems and software programs has echoes of the Y2K computer problem.

In the not-so-subtle tug-of-war of trade rules and technology standards, the globalization of the bar code represents a small erosion of American industrial hegemony.

Europe won this one. The global bar code standard will be the European Article Numbering Code. It turns out that the American Universal Product Code - which turned 30 years old last month - was never so universal after all.

The difference between the American and the European bar code standards, as it so often is in computing, is a matter of digits. When the Europeans set up their bar code in 1977, patterned after the American standard, they reasonably decided that they needed extra digital space for more products and identifying countries. (There were 12 nations in the European Community at the time.)

So the European code has 13 digits, while the code used in the United States and Canada has 12. The 13-digit code took off and is used in most other countries. And the American side has finally made an accommodation with reality. The Uniform Code Council, the North American arbiter of bar codes, has told North American retailers that bar-code scanners will have to read the 13-digit codes by January. The 12-digit codes do not die; systems that can read 13-digit codes can also read 12-digit codes.

"But the 13-digit standard is what it's all moving to," said Ray Tromba, an expert in retail and consumer products distribution for IBM Global Services. "The 13-digit is the global standard."

The bar code's globalization is a sign of its triumph over the years. As the identifying code of modern commerce, it has made possible everything from faster checkout service to sophisticated market research. More than five billion bar-coded products worldwide are scanned every day.

When the bar code arrived three decades ago, the computer revolution was beginning in earnest. Low-cost, powerful computing and vast databases, experts say, helped reduce labor costs, change the relations between manufacturers and retailers and hasten the rise of efficient mass-merchandisers like Wal-Mart - and the bar code was central to that revolution.

"The bar code opened a gold mine of data," said Janice H. Hammond, a professor at the Harvard business school. "Without the bar code, it would be a whole different ballgame in retailing than it is today."