Prices for 1991-model cars and trucks have been ticking upward with Mazda Motor of America boosting prices three times since the vehicles hit showrooms, an automotive journal says.

Automotive News said the latest Mazda increase of an average of $168 per vehicle came on top of earlier average increases of $312 in November and $40 when the cars and trucks were introduced last September.The journal said base prices have been increased twice during the model year by Toyota Motor Sales U.S.A. Inc.; American Honda Motor Co. Inc.; Nissan Motor Corp. in U.S.A., Volkswagen United States Inc.; Audi of America and Volvo Cars of North America.

Among the domestic automakers, Ford Motor Co. raised prices earlier this year by an average of $61 per vehicle on top of a $312 increase at the beginning of the model year.

Chrysler Corp. also has boosted prices twice for 1991 models over the previous year's, and General Motors Corp. raised some of the prices of its options earlier this year.