The world's Y2K jitters are aroused in part by the dawning recognition of a far more serious problem: No matter what happens, or doesn't, this weekend, our high-tech civilization is becoming increasingly vulnerable to significant disruptions, or even collapse.

The bewildering intricacy and interconnectedness of computer networks, energy supplies, financial systems, telecommunications, transportation, law enforcement, manufacturing and even retailing make all of them vulnerable to accidents, errors and attacks. Even a relatively minor failure in one of the "critical infrastructures" upon which our lives, health and property depend can radiate calamity across the nation and even around the globe.

"The year 2000 challenge has served as a wake-up call to many who were previously unaware of our nation's extensive dependency on computers," said Jeffrey Steinhoff, the top technology expert at the General Accounting Office, a watchdog agency of Congress. "However, unlike the year 2000 problem, critical infrastructure protection will be an ongoing challenge."

Sometimes a tiny mistake has horrendous consequences.

In 1997, a programmer loaded the wrong computer tape and brought two of the nation's largest railroads almost to a halt. The blunder came during the merger of the Union Pacific and Southern Pacific lines. It caused a monster traffic jam at a rail yard in Houston that eventually spread through much of the 36,000-mile system and ended up costing more than $1 billion in losses.

Similarly, a missing semicolon in a computer program shut down most of AT&T Corp.'s telephone network for nine hours in January 1990. First, one central switch crashed, then another and another, like falling dominoes, until 50 million long-distance calls were blocked.

"AT&T people were not prepared," said Robert Lucky, vice president of Telcordia Technologies, a telecommunications research firm in Red Bank, N.J. "It never crossed people's minds that the whole network would go down."

Alerted by such incidents and by a surge of international terrorist threats--as well as by the Y2K problem--governments from the White House to city hall are grappling with the need to protect these highly computerized systems. The private sector, too, is increasingly concerned.

"The most critical sectors of our economy are potentially vulnerable to disruptions from computer attack," President Clinton warned last January. He asked Congress for $1.5 billion to address the problem.

Three factors make modern society vulnerable, as never before, to system failures: complexity, connectivity and speed.

* Complexity: Computer networks, airplanes, cars, factories and even home appliances have become so complicated that they often surpass human understanding. "I have two VCRs around the house blinking 12:00, 12:00, 12:00, and I'm an engineer," confessed Lucky, a former AT&T technology executive. "We're building a Tower of Babel that could topple over on us."

A Boeing 747, for example, weighs 165 tons and contains 6 million parts. "No single person can comprehend the entire workings of a Boeing 747--not its pilot, not its maintenance chief, not any of the thousands of engineers who worked upon its design," Robert Pool says in his book "Beyond Engineering." "Such complexity makes modern technology fundamentally different from anything that has gone before."

The auto industry is a frequent victim of increasing complexity. The 1994 Chrysler Neon had to be recalled three times to repair imperfect parts, according to Pool.

Computer software is even more mystifying than hardware. Billions of lines of code churned out by programmers who have retired or gone to other companies might as well be written in Sanskrit. Each new "feature" can cause one or more "bugs" that need fixing.

* Connectivity: The tight links among essential systems increase the risk that a single failure in one sector will also affect many others.

"Since the early 1990s, an explosion in computer interconnectivity has revolutionized the way our government, our nation and much of the world communicate and conduct business," the GAO's Steinhoff told Congress. "The benefits have been enormous. However, this widespread interconnectivity poses enormous risks to our computer systems and, more importantly, to the critical operations and infrastructures they support."

With such tight connections among systems, there is little tolerance for interruptions.

For example, New York City can no longer allow the 12- to 24-hour blackouts it suffered several decades ago "because the financial industry and business community at large are so heavily computerized and dependent on high-capacity communications," said Robert Bell, a retired vice president for research at Consolidated Edison Co., the power company.

* Speed: To paraphrase the Federal Express slogan, nowadays it seems that everything absolutely, positively has to be there right away. In this hectic "7 x 24" era, business goes on seven days a week, 24 hours a day, around the globe. Every time you use a credit card, order a book online, ship something via United Parcel Service, buy or sell stock, send an e-mail, use a cell phone or an ATM, you expect immediate service.

Modern go-go business managers squeeze out inefficiency but also expose systems to serious disruption. "Just in time" is the watchword of today's retailers and manufacturers: It means the security blanket of a comfortable inventory is gone. There is no slack in the system for unexpected delays.

In his book "Faster," author James Gleick describes industry's compulsion for "fast cycle time," the shortening of each step from conceiving a new product to delivering it.

For example, it used to take automakers five years to develop a new model. Toyota now claims it can turn out a new car in 18 months. Turnaround time in the computer industry is even faster. The Austin, Tex.-based Dell Computer Corp. claims that parts spend an average of only eight hours in its factory before they are shipped out in new PCs.

Less than 2 percent of American Airlines' fleet of planes is idle at any one time, reports Gleick, which leaves no backup aircraft to cover unanticipated problems.

"No one can scope out all the interactions," said Orlowski of the National Association of Manufacturers.