When Yoshimi Mitsuya turned on his car navigation system Sunday, he was amazed by the precision of the satellite system that maps the location of his Mercedes-Benz second by second, street by street in Tokyo.

Because of a glitch in the Global Positioning System, the device in Mitsuya's car malfunctioned, just as expected, at precisely 9 a.m.

The blank white screen that greeted Mitsuya was the product of a calendar and computer problem that is said to be something like the Y2K complications that may strike with the arrival of the new millennium Jan. 1.

The failure of thousands of car navigation systems in Japan, despite more than a year of publicity and the offer of a free fix, has some here wondering how well this high-tech society will fare when the big test comes on New Year's Day.

"I guess the lesson is we should all be more responsible and do what we're supposed to do," said a chagrined Mitsuya, president of a company that installs antenna systems in Tokyo. "I didn't pay much attention," he admitted. "I thought it wouldn't affect my unit."

Older car navigation systems that had not been fixed stopped working at 9 a.m. Sunday Tokyo time when the 24 satellites used by Global Positioning System (GPS) receivers, which keep track of the date by measuring the number of weeks elapsed since January 6, 1980, reached their built-in limit of 1,024 weeks and automatically reset their clocks to zero. In Japan, approximately 340,000 navigation systems that rely on the GPS satellites have been sold for cars, taxis and delivery trucks.

In Mitsuya's car, a six-inch video screen mounted near the dashboard shows the exact location of the vehicle as it navigates through Tokyo's labyrinthine streets, most of which are unnamed.

About 95,000 of those units had not been repaired as of yesterday; any still in use showed blank screens or strange locations when their operators turned on the vehicles Sunday morning.

In the United States and elsewhere, there were few reports of problems from the GPS rollover. Officials at General Motors Corp. and Ford Motor Co. said they had not experienced any problems with the satellite switchover, nor had they heard of any outside their companies. Chrysler Corp. said that it does not use the system.

Both GM and Ford said the main reason there were no problems in the United States was that the American automakers were late getting into the satellite positioning business. The receivers used by the industry are newer than much of the equipment used in Japan and had been programmed to deal with the changeover. "We didn't really get started until late 1996," said Geri Lama, spokeswoman for GM's Onstar system.

But the Japanese companies that make the systems have received hundreds of calls in the last two days from people wanting their navigation systems fixed.

"We had 700 phone calls. We are expecting more in the coming days," said Tomomi Akao, a spokeswoman for Pioneer, the largest of four Japanese manufacturers of the car navigation systems.

Early last year, Pioneer started appealing to owners of the units to bring them in for a remedy, which consists of replacing a one-inch black computer chip with an updated version. Pioneer and the other companies say they mailed notices to anyone who had sent in the customer registration card after purchasing a unit, but most buyers had not bothered to do that.

Similarly, critics of the country's Y2K efforts complain that their warnings are falling on deaf ears. A report last year rated Japan as below par in preparedness for the so-called millennium bug, which may cause malfunctions in electronic equipment not programmed to recognize years beginning with 2000. Japan was no more ready than Egypt or Armenia, said the report by analysts of Gartner Group Inc. of Japan.

By March of this year, the same analysts had upgraded their estimation of Japan's readiness, and other observers say the progress has been good.

"Japan has caught up very, very remarkably," said Robert Feldman, chief economist and managing director of Morgan Stanley Japan. "At least in the financial sector, guys who were scared six months ago say they have a lot more confidence."

Still, it was only last month that Prime Minister Keizo Obuchi formed a crisis management team to coordinate the government's Y2K efforts. A task force found that 80 percent of the country's medical institutions, half of the municipal governments and vast numbers of small- and medium-size businesses had not yet dealt with possible consequences of critical computer failures on New Year's Day. And East Japan Railway is not so confident; it will hold its trains at the stations on midnight, Jan. 1 for several minutes.

"Small corporations are a big problem. It's a problem all over the world, and this is where we must expect some problems," said Shumpei Kumon, executive director of the Center for Global Communication at the International University of Japan.

"As far as big corporations and the central government are concerned, the degree of preparedness in Japan may be just as good or even better than in other countries," he said. "But this gives no guarantee that we will escape from the time change difference without consequences."

The consequences of the GPS car navigation system failures were apparently minor: There were no reported accidents, and Pioneer service center manager Tokio Shimanaka said none of his customers reported getting seriously lost.

And he said at least one customer neglected the repair on purpose: "He said he knew exactly the problem, but he didn't get it fixed because he wanted to see what would happen," Shimanaka said. "And just like it was supposed to, it failed."

Special correspondent Shigehiko Togo contributed to this story from Tokyo, and staff writer Frank Swoboda contributed from Washington.

CAPTION: A customer checks a portable Global Positioning System receiver at an electronics shop. About 340,000 Japanese have in-car navigation systems.