Not so long ago, a Y2K computer catastrophe seemed inevitable. Few believed that the world's businesses, governments and technicians could band together to test hundreds of millions of computers and tens of billions of electronic devices, painstakingly fix any problems and then check them all again to ensure the repairs worked.

Even the most optimistic specialists predicted moderate disruptions: Some cities would certainly lose power. Phone systems might fail. Banking records could disappear.

But when clocks rolled into 2000, and officials from New Zealand to Hawaii checked their monitors, even the most sanguine forecasts seemed too dire, leading many to question why the much-feared Y2K glitch was such a dud--even in Russia, China, India and other nations seen as particularly vulnerable to failures.

So what went right?

Technology analysts offered a combination of answers yesterday. They credited the unusual cooperation among businesses and governments worldwide to address the issue. They cited the unprecedented mobilization of people, money and executive attention for the repair effort. And they wondered whether some of their previous assumptions--specifically about the technological dependence of less-developed countries--had been off the mark.

"We may have overstated the impact of technology on the infrastructure in a lot of developing countries," said Matt Hotle, a vice president at the Gartner Group, a technology consulting firm that predicted early last year that Y2K could create "significant disruptions" in such nations.

In Paraguay, for instance, where the government waited until mid-1999 to start tackling the glitch, the country's Y2K coordinator had predicted widespread power outages, water shutdowns and phone disruptions. But as of yesterday afternoon, all basic services, including electricity, telephones and water, were functioning normally.

"At this moment, everything is working," said Walter Schafer Paoli, the former coordinator. He attributed the poor, landlocked nation's success with Y2K to redoubled efforts to fix computers in the final weeks of 1999 and a discovery that many government services were less reliant on computers than initially thought.

"When they began to do the repairs, they found the problem was not as bad as they believed," Schafer said.

The same assessment was given yesterday by officials in Washington, who expressed surprise that there were no reports thus far of major disruptions in Russia and China. "I think the reason we're not seeing anything too serious there is that the systems in those countries were not highly vulnerable to the Y2K bug in the first place," said Bruce McConnell, the director of the International Y2K Cooperation Center, a United Nations-funded organization that has been closely monitoring date-related problems.

The civil infrastructure--the power, water and phone systems--in those countries often does not depend heavily on computers, he said. And in some cases where it does, foreign governments and businesses have been able to accomplish their repair work in a shorter time than their American counterparts because they opted for programming shortcuts that are less common in the United States, such as rolling a computer's internal clock back to 1979, because the days of the week match those of 1999.

With regard to the United States and other developed countries, industry executives and government officials cited the massive outlay of cash--estimated at $100 billion domestically and a half-trillion dollars worldwide--that was spent to hire programmers and buy new computers. They defended the spending yesterday as necessary to deal with the Herculean technology challenge.

"I don't know anyone who's spent any time on this problem at all who doubts that, had the effort not been made, had the money not been spent, we would be in a very different situation here right now," said White House Y2K czar John A. Koskinen.

In the District, which earmarked $140 million to wipe out Y2K bugs, city officials kept an old Department of Public Works computer application running into the new year--even though it had been replaced by a new system. Sure enough, just after midnight, it listed the year as 1900.

"The fact I think we haven't seen many problems was not because there really wasn't a Y2K issue," said Mayor Anthony A. Williams (D), who called the glitch "a once-in-a-lifetime event."

"It threatened the very foundation and infrastructure of the city, the basic delivery of services in the public and the private sector," Williams said. "It's very, very hard to say what cost is too high. You know no one's doing a cost-benefit analysis of Normandy. We had to do Y2K. It's on that order of magnitude."

Although much of the Y2K spending was devoted to simply making older computer systems operate normally this year--the electronic equivalent of patching a flat tire--some of the money went for new machines that likely will make businesses and government agencies more efficient. The repair effort also has given many organizations, for the first time, a census of all their computer systems and helped them weed out antiquated technology.

"We know ourselves technologically better than at any time before," said Rear Adm. Robert Willard, a Y2K coordinator at the Defense Department, which spent $3.6 billion on Y2K preparations.

After almost a full day to monitor computer systems, U.S. government officials yesterday reported a series of minor Y2K glitches scattered across the country as well as one potentially serious disruption: A military reconnaissance satellite system was inoperable for several hours last night.

The problem hit a ground-based computer system responsible for processing data from a network of intelligence satellites shortly after the rollover passed midnight Greenwich Mean Time (7 p.m. EST), which is the time standard for many satellite systems, Deputy Defense Secretary John Hamre said.

The processing station had been extensively tested, but not when the satellites were in the configuration they were in on New Year's Eve, defense officials said. Simulations did not pick up a problem that developed in the combination of the date rollover and positioning functions, the officials said.

By yesterday afternoon, the processing station was still not at "normal peacetime operation." Pentagon officials would not disclose the nature of the intelligence gathered by the satellites.

Other minor Y2K-related errors hit seven nuclear plants, including one in Arkansas where workers were denied entry through automatic doors because a Y2K software patch had not been installed on a radiation monitoring unit. None of the problems affected safety systems, officials said.

Wind-shear alert systems failed at airports in Tampa, Denver, Atlanta, Orlando, Chicago and St. Louis during the midnight rollover, but technicians were able to quickly re-start the systems to clear the error. Several electric utilities also reported glitches with clocks used to synchronize management systems. And in Omaha, a security access system malfunctioned at a federal building, freezing doors in the open position; to get the doors to shut, technicians reset the computer clock to 1972.

The absence of more serious disruptions pleased government officials. At a news conference yesterday afternoon, Koskinen gushed that the nation was in "much better shape than anyone would have predicted."

Still, Koskinen and others cautioned that additional problems probably will be discovered on Monday--and through the next several weeks--when companies and government agencies reopen for business. "It's far too early to declare victory," Koskinen said.

McConnell, of the international Y2K center, warned that organizations still could face some "inconveniences, headaches and hiccups over the next few days."

That was a message voiced even more strongly by people who believed the Y2K glitch would cause serious disruptions, even in the United States. Paula Gordon, a visiting research professor at George Washington University who earlier this year wrote a paper asserting that "Y2K is not a solvable problem," maintained yesterday that serious trouble could still occur over the next several months as hidden errors degrade computer systems.

"There will still be a major fallout," Gordon argued. "We should not be lulled into thinking this problem is over."

But other Y2K skeptics expressed surprise and relief yesterday about how smoothly the switch to the new millennium has gone, with no regrets about the hundreds of gallons of water they collected, along with the canned food, batteries and backup heaters.

In fact, some of the naysayers gave themselves credit for the glitchless Jan. 1. "If we had sat around and said nothing, we might all be sitting in the dark," said Burke resident Gail Fialkow, secretary of the Northern Virginia Y2K Community Action Group, which encouraged area residents to stockpile goods for the inevitable chaos it believed would occur when 2000 arrived.

Jay Golter, the group's leader, said that "in hindsight, some of the things I did were not necessary, but if you replay the tape, I'm not sure I'd do much different."

Golter, who said he was not surprised by how smoothly the transition went in the United States but had expected serious problems in other areas in the world, stocked more than 100 two-liter bottles of water and attached large barrels at the end of his four downspouts.

He now intends to use the water in his garden. And he's sure his family will use most of the canned food he bought, although he said he wouldn't have purchased a $600 wood stove if it weren't for his concerns about Y2K.

In a few weeks, his Y2K group will hold a potluck dinner. "Perhaps we'll have rice and beans"--commonly stockpiled fare--"or we might use that as an occasion to drop off the extra food at a food bank," he said. After all, he noted, his family is not fond of all the bags of dried beans he bought as a precautionary measure.

Staff writers Stephen Barr, John M. Berry, William Claiborne in Chicago, Caroline E. Mayer, Sylvia Moreno, Don Phillips, Michael D. Shear, Alan Sipress, R. Jeffrey Smith in Rome and Roberto Suro contributed to this report.

CAPTION: D.C. Mayor Anthony Williams, left, talks with Carl Mecca, center, and Leon Jackson from the Office of the Chief Tech Officer as reports come in early yesterday.