Planning an automobile trip over the Labor Day weekend? If so, you'll find the average price of gasoline has risen less than one-half cent a gallon since the Fourth of July holiday, according to a new survey by the Fairfax County-based American Automobile Association.

The current national average price of gasoline -- averaging the two basic grades of gasoline and the differences between self-service and full-service costs, and including taxes -- is $1.318 a gallon, a rise of 0.4 cent since July 4.

That contrasts with an 8-cent rise in the five weeks between Memorial Day and July 4. The current price is about a nickel below a year ago.

If you fill up in the District of Columbia or its suburbs, the average self-service prices are $1.213 a gallon for regular and $1.272 for unleaded.

The comparable full-service prices are $1.409 regular, $1.464 unleaded. That's an overall average of $1.339 a gallon, 2.1 cents above the national average and highest in the mid-Atlantic region.

The average for Maryland, outside the Washington area, is $1.275; for Virginia, it is $1.337.

The lowest average price in the nation, at $1.248, is New Jersey -- which seems incredible, since that state (along with only Oregon) has no self-service stations. The full-service price for regular is $1.218; for unleaded, $1.278. (Note that self-service prices in the Washington metropolitan area are, in fact, lower.)

The biggest bargain on the Eastern Seaboard still is Delaware: its self-service average prices are $1.157 for regular, $1.214 for unleaded.

Highest prices in the 48 contiguous states are charged in a state unlikely to be visited by weekend drivers from Washington. That's California, where the average is a startling $1.421.

The AAA said its survey covered 6,000 service stations along major travel routes.