DETROIT (AP) _ Porsche Cars of North America Inc. said Wednesday that 1988 base sticker prices for its luxury roadsters range from $25,910 to $81,785, up 2 percent to 3.9 percent from final 1987 prices.

The new prices became effective Tuesday when stickers on all 911 models and the 928S-4 increased 2 percent, and prices on all 924 and 944 models went up 3.9 percent.

Porsche had planned to increase all prices by 3.9 percent for 1988 but decided on lower increases for six- and eight-cylinder engine models in November, spokeswoman Martha McKinley said.

The West German luxury sports car maker also decided to cut production by about 10 percent, or 4,900 cars, next year, she said.

Both decisions were in response to the October stock market collapse and to Porsche's worldwide sales projections, she said.

Porsche expects to sell 25,000 cars in the United States by the end of this year and 20,000 in 1988, she said. In 1986, Porsche's U.S. sales topped 30,000.

''We like to maintain flexibility. If we have to increase production again, we'll do that,'' McKinley said.

The least expensive Porsche is the $25,910 924S with manual transmission, which carried a final 1987 price of $23,910. The most expensive is the $81,785 911 Turbo Cabriolet, which was not available in 1987.