The price of diesel fuel in the Washington area has soared to the highest level in the continental United States, according to this week's auto club survey of more than 6,000 gasoline stations.

Diesel prices here are more than 7 cents higher than the national average and have surpassed average gasoline prices in Washington for self-service regular and unleaded grades.

The survey, compiled by the national office of the American Automobile Association (AAA), was conducted Monday through Wednesday by telephone and released yesterday.

Government and industry officials were reluctant to speculate why prices are higher at the approximately 35 Washington area stations that sell diesel fuel. However, if the AAA survey is borne out by other, more extensive surveys, the results would support the widely held contention that Washington has been more affected than most cities by the current fuel shortage.

The results will particularly annoy the hundreds of Washington area motorists who have purchased diesel-powered automobiles in recent months, hoping cheaper diesel fuel, greater fuel economy and more plentiful supplies would insulate them from gasoline lines and rising prices.

During the first six months of this year, 147,109 diesel passenger cars were purchased nationwide compared with 135,570 sales for all of 1978 and 41,189 sales in 1977.

Diesel fuel models are marketed in the United states by Oldsmobile, Cadillac, Mercedes, Peugeot and Volkswagen.

"The price of diesel (fuel) has gone up much faster than gasoline prices," said Mary Ann McCarthy, a retired government worker who bought her Mercedes 200D in 1968. "I bought it because it would be cheaper to operate...and with the intention of keeping it the rest of my lifetime," McCarthy said. "Now," she added, "whenever I can use public transportation, I do that."

The AAA survey showed that diesel prices range from a low of 89.9 cents a gallon to 104.9 cents at Washington area stations for an average price of 95.4 cents.

The national average price this week was reported at 88 cents a gallon, up 1.4 cents from the previous week.

"The only thing close (to the Washington price) is Mississippi with 94.6 cents a gallon," said an AAA spokesman.

Though prices of gasoline and diesel fuel have gone up sharply since the first of the year, diesel, unlike gasoline, is not subject to government price controls. Theoretically, the price of the heavier fuel is more responsive to changes in supply and demand.

Earlier this year, shortages of diesel fuel and rising prices sparked sporadic violence among the nation's truckers, who remain dissatisfied that the government is doing enough to help them.

Truckers use nearly 12 billion gallons of diesel fuel a year and federal energy officials have been expressing concern for months that major oil company reserves of diesel fuel are dangerously low and may lead to further shortages this fall and winter.

Moreover, since diesel fuel is almost identical to home heating oil, truckers and diesel car owners could find themselves competing with the nation's furnaces for adequate supplies this winter.

Diesel and home heating oil are lumped together under a category called "distillate" by refiners.

"We're scared to death," said Lana Batts, director of the department of economics and planning for the American Trucking Association. "We know when push comes to shove, the home heating oil user is going to get it (fuel). There's no politician in the world who's going to have cold homes and the freight running."

The U.S. Department of energy has expressed more optimism in recent weeks that refinery reserves of diesel fuel and home heating oil are increasing at a rate that will provide a margin of safety by the time cold weather sets in, but tight supplies may well keep prices at extraordinarily high levels.

"A quarter of the trucker's diesel is now being bought on the spot market at (per gallon) prices exceeding $1," said Batts.

High diesel costs have also plagued mass transit systems. Washington's Metro had set aside $6.5 million to fuel its Metrobus fleet in the fiscal year that began July 1. However, because of skyrocketing prices, new estimates put the diesel fuel expense at $10 million, an increase of 54 percent.