Northern Virginia is the most expensive place in the Washington area to buy gasoline, and the price gap is widening, the American Automobile Association said yesterday.

In one month, gasoline prices in the Virginia suburbs jumped a nickel to an average price of $1.42 per gallon, an AAA survey of 100 area service stations showed.

By comparison, the average price of gasoline pumped in the District rose less than a cent a gallon, and Maryland gasoline fell a half a cent.

An AAA spokesman said the 2.2 million motorists in the Washington area are paying an average of $1.37 a gallon in the District and $1.35 in Maryland. Prices of the various grades of gasoline also vary by region.

"It drives me crazy; the prices change so much I spent more time looking for gas stations than I do women," said Jeffrey Allen, a laborer working in Alexandria.

Last week Allen drove to the Maryland shore, and he said that almost every station he passed displayed a different price.

"But I did notice low prices in Maryland. Well, not really low, but lower."

Betty Rice, a U.S. Bureau of Labor Statistics analyst, says that the Washington area is the fourth most expensive area in the nation in which to purchase gasoline. Of the 28 metropolitan areas studied, only San Francisco, San Diego and Honolulu are more costly for car fuel.

"Virginia has always been more expensive," said Vic Rasheed, the executive director of Service Station Dealers of America. "They're not as competitive because they allow refiners to sell gas retail."

The District and Maryland implemented laws in recent years forbidding refiners to own and operate gasoline stations there. Rasheed, whose organization represents 60,000 dealers, said the reason that the District's average price is higher than Maryland's is probably a District law that requires that vapor-recovery hoses be used at the pump. These heavy pumps cost several thousand dollars and translate into higher pump prices, Rasheed said.

Dan Lunberg, publisher of the Lunberg Letter, a weekly statistical roundup of petroleum prices, said from his Houston office yesterday that nationwide gasoline prices have risen at least 2 cents a gallon because of Environmental Protection Agency rules that will take effect Monday.

The EPA rules require that, by Monday, the lead content of regular gasoline be reduced to 0.5 gram per gallon. By Jan. 1, the maximum legal lead level will be 0.1 gram per gallon, and, because of health concerns, the EPA has asked that all lead be removed from gasoline eventually.

Rasheed said most dealers, anticipating the lead reduction phase, have raised prices and begun replacing lead -- which enhances the power of gasoline when burned -- with a more expensive octane enhancer, alcohol.

For every penny in the rise of a gallon of gasoline, motorists pay $1 billion more each year, Rasheed said. "That's one pretty expense tab."

AAA spokesman Doug Neilson said that, nonetheless, automobile travel during the July 4 week is expected to be higher this year than in past years. "The price isn't as restrictive as in the past," Neilson said. "In 1981 it was $1.44 a gallon and people just stopped traveling cross-country. Now we're getting lots of calls from people traveling long distances."