The way gasoline prices have been rising lately, the 5-cents-a-gallon increase in the federal gasoline tax scheduled for Dec. 1 under the budget agreement probably will seem like more of the same.

Few motorists are likely to realize that the extra nickel is the result of federal government efforts to balance the budget rather than oil company attempts to catch up with the rising price of crude oil.

The price of a gallon of gas has jumped 30 cents or more since Iraq invaded Kuwait Aug. 2, and most analysts expect it to continue rising to catch up with spiraling crude oil costs. The American Automobile Association says the average price of self-service unleaded gasoline, the most popular grade, is $1.38 a gallon; the Lundberg Letter, a gasoline marketing newsletter, reckons that the average for all grades is $1.47 a gallon.

At those levels, another nickel for taxes is likely to get lost in the shuffle. Consumer advocate Ed Rothschild, executive director of Citizen Action, and other analysts said the relatively small tax increase probably will not affect overall consumption very much.

To the average driver, who motors about 15,000 miles a year and gets 22 miles to the gallon, the increase in the federal gas tax from 9 cents to 14 cents a gallon will add a bit more than $34 to annual automobile operating costs. Motorists with high-mileage cars that they use just to get around town will pay about half that; long-distance drivers with low-mileage cars will pay around $25 more than the average.

And some experts say the structure of the new gas tax could have an impact on motorists that goes beyond the pocketbook. The American Automobile Association, which has lobbied against the use of a gas tax to reduce the budget deficit, said the higher tax should be used to pay for road improvements, and others would like to see it used for mass transit.

MPG...........10,000..........15,000..........20,000

17............$29.41..........$44,12..........$58.82

22.............22.73...........34.09...........45.45

27.............18.52...........27.78...........37.48

29.............17.24...........25.86...........34.48