Foreign and domestic auto makers, their spirits boosted by record 1985 sales, see 1986 as another good selling year in the United States.

But some auto industry analysts believe manufacturers will have to keep sales incentives going to keep customers coming into showrooms.

Auto makers sold 15.7 million cars and trucks last year, surpassing the previous record year, 1978, when they sold 15.4 million.

"We expect 1986 to be another good year for the industry, with U.S. sales again exceeding 15 million units," said General Motors Corp. Chairman Roger B. Smith, echoing a prediction made by other auto makers selling cars in the United States.

But analysts say that much of last year's success was attributable to cut-rate financing programs and booming consumer demand for light trucks -- pickups, full-size vans, minivans and utility vehicles.

The truck craze is a welcome development for auto makers and suppliers, both of whom are cashing in on the growing acceptance of trucks as multipurpose vehicles. But cut-rate financing and other sales-incentive campaigns constitute a bad habit, one that conceals weaknesses in the market, some of the analysts say.

"There's still a bit of hype out there that has kept the market buoyed up a little bit more than where it should be," said James A. Mateyka, vice president for automotive analysis at New York-based Booz, Allen & Hamilton Inc.

"You can't continue to hype the market forever. Eventually, you'll run out of buyers," Mateyka said.

The underlying softness in the domestic auto market probably will show up in 1987 and 1988, largely because of an influx of foreign cars that will make the market "horrendously competitive," Mateyka said.

In that environment, new-car buyers will have the upper hand, and the car companies will have to spend more money to sell more products, according to a recent editorial in Automotive News, a weekly auto industry trade journal.

"The customer has trained Detroit very well," the trade journal said. "He will buy a car during an incentive period. When Detroit stops, so does he. After a long enough period to convince Detroit that the customer means business -- by not buying -- Detroit offers another 60-day period of incentives. And the cycle begins again."

Foreign-car manufacturers, particularly the Japanese and Germans, did not use incentives as much as their U.S. rivals in 1985. But the foreigners may have to increase their trips along the incentive route to hold their share of the market, according to analysts at J. D. Power & Associates, a California-based auto-market research firm.

"Lower . . . prices will come in the form of significantly more price-leader models from Japanese manufacturers, which will begin taking the low-priced market more seriously" as Third World auto makers begin shipping cars to the United States, the research firm said of the 1986 domestic market.