TOKYO -- Japanese motorists navigating through their weblike cities and nameless streets are looking beyond the sky to find the way round the next corner.


Introduced four years ago as a novelty, navigation systems that use satellites to locate a car's position on an electronic map are fast becoming something that has eluded electronic-gadget makers since the 1980s: a smart new product consumers actually want to buy.


Sales are expected to double to 300,000 this year, according to makers and industry analysts. As prices fall and new features are added to avoid traffic jams, they are forecast to reach half a million in 1995 and a million by 1998.


Unlike the rest of the world, in Japan the systems have caught on -- and if not yet commonplace, they are no longer regarded as just a novelty.


One reason for the late start outside Japan is that maps were put on CD-ROM earlier in this country than anywhere else. Another is current laws in various countries that ban television-type displays that could distract a driver.


The systems process signals from 24 so-called global positioning satellites, launched by the U.S. military, and can tell a car's position to within 30 meters.


Each satellite contains an extremely accurate clock, and gives out signals stating the time at which they are sent. Earthbound receivers use their own clocks to work out, from the time it took the signal to arrive, how far away the satellite is.


As the car is known to be on earth's surface, knowing the distance from three satellites is enough to determine uniquely its position, although a fourth is usually used to provide a check.


The position is then displayed on a liquid-crystal display map stored digitally on compact disc: the CD-ROM method.


Marketers say people are not just buying the systems for navigation but as in-car entertainment units.


For urban Japanese, with a choice between fast, punctual public transport and miserable traffic jams, a car is not so much a way of getting from A to B as a personal space to make up for the lack of privacy in cramped homes. Businessmen cover the seats of their Mercedes with doilies, and young women arrange teddy bears and cushions in the back.


The navigation systems also play CD-ROMs with information on hotels and golf courses, music, and even karaoke.


"Our main customers are in their 20s," says Noritaka Murata, a marketing manager for navigation systems at Pioneer Electronic Corp., the joint market leader with Sony Corp., with about 40 percent of the market.


"They have more disposable income than the middle-aged -- and nice cars."


The trend can be seen with Fujitsu Ltd.., which is approaching it from the other direction. It launched a navigation version of its video-game machine, called "Car Marty."


Pioneer's Murata expects the market really to take off in a few years, when the price falls and performance improves.


He says the product is basically like a personal computer, made up of electronic components such as chips and an LCD -- one of the most expensive parts -- the costs of which all slide with volume production.


The first machines cost 700,000 yen ($7,000) and are now down to 250,000 yen. By 1998 the price will probably dip below 100,000 yen, which was the critical level for a succession of consumer electronics products to take off.


The latest models come with an autonomous positioning unit to supplement the satellite receivers. When a car enters a tunnel, sensors calculate its location using its speed, direction, and the time since it lost touch with the satellite.


Also, from 1996 they will pick up and electronically digest traffic information gathered by the police and relayed by FM radio signals: Tell the system where you want to go and it will find its way round one-way streets and choose routes avoiding the worst traffic jams.


Some analysts are not convinced the navigation systems will catch on as easily outside Japan.


Roads in Europe and the United States are not as crooked as those in Tokyo and Osaka. And they tend to be clearly labeled with names, unlike in Japan, where addresses are given in terms of a complex system of blocks.


Finally, Europeans and Americans do not appear as keen as the Japanese to beautify the insides of their cars.


"Theft is a not a problem in Japan," says Yoshiharu Izumi, an analysts at UBS Securities' Tokyo office. "In Europe and the United States, visible expensive gadgets may increase the chances of a break-in."