NEW YORK -- Y2K computer worries won't go away this weekend, even if nothing goes wrong. Glitches are likely weeks, even months, into the new year. And a few may linger until 2001 and beyond.
The Gartner Group, a technology consulting firm, estimates only 10 percent of all Y2K failures will occur during the first two weeks of January.
Yet an Associated Press poll taken earlier this month found that only 16 percent of respondents think Y2K problems will last more than two weeks. And the number who think the problems will be confined to less than a few days has increased from 22 percent to 36 percent.
Most Y2K planners are aware that Jan. 1 is no magic date, but they fear a quiet weekend might leave the public with a false sense of security.
"There is too much focus on New Year's weekend," said Bruce McConnell, director of the International Y2K Cooperation Center. "If you think that the only time to worry about the Y2K bug is on Jan. 1, then you're underestimating the problem."
Besides having new problems appear later in the year, glitches that strike on Jan. 1 might go unnoticed initially, even after employees return to work and restart computers. The full effects might not be felt until smaller glitches compound and disrupt business supply chains.
Several weeks must pass, McConnell said, "to have a good idea just how big an event Y2K is."
Ron Weikers, a Philadelphia attorney specializing in Y2K litigation, warned companies not to declare victory right away. Such statements, he said, could come back to haunt them.
Still, New Year's Day weekend will be a peak period for Y2K problems, and most major companies and government agencies will be watching their systems closely. John Koskinen, President Clinton's top Y2K adviser, will preside over a $50 million crisis center built for this weekend.
If there are any problems involving embedded chips that control power plants and other major equipment, Koskinen said, they would most likely strike around Jan. 1.
Beyond that, most glitches will probably be administrative, causing inconveniences such as incorrect billing -- but no catastrophe. And they'll be more manageable because they won't hit all at once.
The government has identified three crucial time periods:
-- Dec. 31, when the rest of the world celebrates the new year;
-- Jan. 1, when the new year arrives in the United States; and
-- Jan. 3, the first business day, when systems experience peak usage.
Koskinen's group will also look for trouble on Feb. 29, because some computers might not recognize 2000 as a leap year. Even Dec. 31, 2000, could be problematic because some computers might not be expecting 366 days next year.
The Y2K problem stems from a long-standing practice of using only two digits to represent a year in computer programs and embedded chips. Left uncorrected, "00" might appear as 1900, throwing off systems that control power, phones and billing.
In an AP telephone poll of 1,010 people, taken Dec. 15-19, the most frequently mentioned concern was the power supply, mentioned by a third, followed by banking and financial services, the transportation system, phone systems and food distribution. The poll's margin of error was plus or minus 3 percentage points.
Jan. 1 is not necessarily the first time a computer will encounter 2000, and some problems already have appeared.
A few years ago, some merchants began having trouble with credit cards expiring in 2000. In early October, some federal computers needed repair because Oct. 1 starts the federal fiscal year.
And in a twist from Maine, model 2000 cars were incorrectly marked horseless carriages -- the designation that the state uses for pre-1916 vintage vehicles.
Notices with 1900, not 2000, also have come from banks, courts and at least one college.
Some problems also occurred during Y2K testing, or as Y2K fixes introduced new errors.
The National Federation of Independent Business cites a recent survey that Y2K already hit one in 20 small businesses. Most glitches were fixed quickly, the federation said.
According to the Gartner Group, 30 percent of all failures will have occurred before 2000. And problems, growing steadily each quarter, will peak early in the new year. But they won't completely disappear until after 2001.
"Systems only fail when transactions are run," said Lou Marcoccio, Gartner's research director.
For example, glitches may arise when businesses finish their first billing cycle of the new year. That could happen anytime in January for monthly billing, or later for less frequent billing.
Some computers will also have to generate monthly, quarterly and annual reports, leaving room for problems later in the year.
-- Federal court officials in Atlanta recently issued summons requesting about 167 potential jurors to report for jury duty Jan. 3, 1900. Authorities say an employee accidentally used an outdated version of jury selection software. Philadelphians also received incorrect jury summons. A homicide detective in Hamilton County, Tenn., was subpoenaed to appear for a case in January 1900.
-- The English Department of the University of North Dakota issued a preliminary schedule for next fall, showing a professor teaching a course about James Joyce in the fall of 1900, when the author was still a student in Ireland.
-- A water reclamation plant near Los Angeles spilled millions of gallons of sewage into a park during a Y2K test in June. The spill happened while the plant was testing a Year 2000 scenario in which the power failed. The emergency generator kicked in as expected, but a gate failed to reopen.
-- About 3,600 water customers in West Des Moines, Iowa got bills saying there will be an extra charge for payments made after Jan. 3, 1900. In the East, Bell Atlantic also sent out more than 300 phone bills with wrong due dates.
-- Oct. 1, the start of federal fiscal 2000, brought problems to four federal agencies. A purchasing system at the Energy Department temporarily failed. The National Science Foundation reported problems with a system that provides information to grant recipients. The Justice Department and Federal Aviation Administration each had problems with budget-related computers.
-- In Maine, owners of 2000-model cars and trucks received titles identifying their new vehicles as "horseless carriages," the designation used for vintage vehicles produced before 1916. About 800 passenger car titles and about 1,200 tractor-trailer titles were issued with the error.
-- Wells Fargo & Co. mailed 13,000 renewal notices to customers in 10 states, saying their certificates of deposit would expire in January 1900. Bank officials blamed the glitch on a printing vendor.
-- Hershey Foods Corp. faced distribution delays because of trouble with a new $112 million automation system designed in part to avoid Y2K problems. At the height of problems in October, several retailers were reporting shortages that forced them to turn to other candymakers to fill bare shelves.