THE NEW CARS - IMPORTS. Imports roll off assembly lines from Brazil to Taiwan, Canada to Romania.

BEFORE long, you may need a world atlas to buy a new car. A tidal wave of imported vehicles is rolling across the United States from low-labor-cost countries whose auto-assembly workers average $3 an hour or less. The trend is viewed as a major threat to the established higher-cost producers around the world.

Already this year, low-priced small cars have been introduced to the North American market from Mexico, Taiwan, and Brazil. In 1986 the first cars from South Korea and Yugoslavia hit US roads.

India joins the list in the fall with a 4-wheel-drive utility vehicle, the Mahindra, while another importer is planning to bring in cars from Romania. Dutch and Malaysian cars are due early next year.

With the runaway success last year of the Hyundai Excel from South Korea (168,882 sales established a first-year import record), three more Korean challengers have reached the lucrative US market so far this year. Chrysler, unsuccessful in landing rights to a Korean-made car, is reportedly negotiating with a manufacturer in Thailand.

The 18-month-long spurt in the value of the Japanese yen has played a role in boosting the attractiveness of cars from low-labor-cost countries.

Most Japanese automakers have increased their prices to US consumers four or five times in the last year and a half, helping to open the entry-level market to cars from South Korea, Latin America, and East Europe (see story, Page B11).

With Japan's export quota of new cars to the US frozen for the third year in a row at 2.3 million, starting April 1, the Japanese are looking for other avenues to the US market. Mitsubishi, for example, has begun to ship cars to the US from South Korea's Hyundai, in which it has a 15 percent stake, while Mazda's 323 subcompact has spawned derivatives being imported by Ford from Mexico, Taiwan, and South Korea. Ford owns 25 percent of Mazda.

And even more Japanese companies are getting in on the act. Japan's ninth automaker, Daihatsu, in which Toyota has an equity position, applied to enter the US market this year with its Charade minicompact.

In addition, the Japanese are overcoming the persistent quotas by expanding North American assembly operations. Honda, Nissan, and Toyota already build cars in the US. They'll be followed in the fall by Mazda and next year by Mitsubishi and a second Toyota assembly plant. In 1989 a joint Subaru-Isuzu plant is scheduled to open.

Imports from all sources boosted their share of US new-car sales in 1986 to 28.3 percent, from 25.7 percent in 1985. While the Japanese slice of the import total stayed virtually flat because of the quotas, the so-called ``Euromakes'' and Hyundai, among the imports, accounted for 1 car in 4.

More impressively, all European makes except Audi, Renault, and Peugeot sold more cars in 1986 than they sold in '85. Eight climbed to new US records: Volvo, Mercedes-Benz, BMW, Saab, Yugo, Porsche, Merkur, and Alfa Romeo.

Unfettered by export quotas across the Atlantic, the European upscale entrants are countering the wave of new-nation imports with added models of their own. Volvo has introduced the Bertone-styled 780 two-door sedan at the top of its US line and is planning to introduce its first front-drive car next winter with the Dutch-built 480ES. BMW has restyled its top-of-the-line 735i series for 1987.

Three new models are on tap for this spring from England: Jaguar's redesigned XJ6 and two new-to-the-US vehicles bearing Rover roots, the Range-Rover 4-wheel-drive utility vehicle and the Sterling luxury sedan, twin of the Honda-built Acura Legend.

Lincoln-Mercury's Merkur line will add the 4-door Scorpio luxury sedan to the Merkur coupe, introduced in the US two years ago.

First-year sales of the midsize Legend and its lower-priced Integra compact line, built by Honda in Japan, reached nearly 60,000 in the US in 1986 and triggered a speedup of plans by other Japanese importers to build full-size sedans.

Other European newcomers to the US in 1987 will come from West Germany, France, and Italy.

American Motors' Renault partner has already introduced the Medallion compact sedan and station wagon, while the Alpine sports coupe and intermediate-sized Premier will arrive later in the year.

These plans will go ahead, according to a AMC spokesman, regardless of Chrysler's recently announced purchase of American Motors.

Alfa Romeo's new Milano sports sedan propelled the US's only Italian import to record sales in the US in 1986.

How high will all these present and future imports send US import sales?

A record 3.6 million cars, either imported or assembled in this country by foreign-built producers, were sold in 1986, up 16.3 percent from the previous year. That's equal to 31.5 percent of the total US market.

All the new imports, plus the added ``transplants'' entering domestic production, could boost the combined total above 4 million cars this year and 4.5 million by the end of 1988 - not counting import trucks and utility vehicles.