American paid 14.2 cents, or 13 percent, more for a gallon of gas in December 1980 than they did in January of that year, according to the American Automobile Association.

The national average price for al grades of gasoline as full service and self service pumps reached $1.246 in December 1980- up from $1.104 in January 1980, AAA said.

The 21-million member motoring federation monitors gasoline prices and availability through its periodic "Fuel Gauge" reports.

The price jumped 15 cents a gallon during the first seven months of 1980. AAA reports Between August and November, however, prices dropped fractionally each moth resulting in a decrease for the four month period totaling 1.8 cents a gallon or 1.4 percent. The decline in gasoline prices, AAA says, was due to intense competition among retailers and the increase in crude oil supplies. Prices edged up one cent in December, according to AAA's Fuel Gauge summary report of 1980 gasoline price performance.

Gasohol, the alcohol and gasoline mixture sold in some states, climbed 14.2 cents, or 12.3 percent, for 1980 rising from $1.156 a gallon in January to $1.298 a gallon in December.

Diesel fuel users paid 10.1 cent a gallon more by the end of 1980. Diesel furl was $1.045 in January. It reached $1.146 in December, an annual increase of 9.7 percent.

Texas had the lowest average gasoline prices for most of 1980, with Illinois and Mississippi recording the highest average prices in the nation for most months during 1980.

AAA's Fuel Gauge report is compiled through a survey of about 6,000 service stations along major travel routes throughout the United States.

FUEL GAUGE SUMMARY REPORT 1980