The average price of gasoline in America crept over the $1 mark last week, according to an authoritative industry survey released yesterday.

It was a milestone that the Department of Energy had predicted as recently as June would not come until much later.

In the Washington area, the average price of gasoline at full service pumps was up about three cents from an identical survey July 20. But those prices still hovered below the $1 mark at an average of 99.6 cents for all grades.

Dollar-a-gallon gasoline has been around since last spring, but last week's survey marked the first time that the national average price of regular, unleaded and premium grades crossed the $1 threshold.

"We had predicted that prices would probably hit $1 by Labor Day, but $1 gasoline is here," said Dan Lundberg, whose Lundberg Survey checked prices at 17,000 stations last Friday and computerized the sampling during the weekend to determine average prices for dozens of cities.

The average gallon of gasoline was going for 100.32 cents Friday, a 50 percent increase over the national average price of 67.1 cents at the first of the year, according to Lundberg.

The full survey results will be published at the end of the week by Platt's Oilgram, an oil industry newsletter.

Lundberg's results clearly show that federal energy officials substantially miscalculated the extent to which major oil compainies would raise prices this year.

Former deputy energy secretary John F. O'Leary predicted June 8 that gasoline prices would go up about a nickel by the end of the summer.

Instead, they went up about 16 cents, more than three times O'Leary's projection.

Federal energy officials also have said that only about half of the 33-cent-a-gallon price increase since January can be attributed directly to increases in the cost of crude oil from the Organization of Petroleum Exporting Countries.

The rest partly represents what one official called "increased profit-taking" by refiners, middlemen and retail service station dealers.

DOE froze the gross profit margins of retailers Aug. 1 at 15.4 cents a gallon, more than twice the average profit level at the beginning of the year.

Before Aug. 1, a loophole in DOE pricing regulations on gasoline had allowed many dealers to collect profits above price-control ceilings to make up for profits not taken during previous years when competition kept prices down.

Another factor in the higher profits was the gasoline "Tilt," a little known federal regulation adopted last March 1. The Tilt rule allows refiners to collect an additional 10 percent profit on crude oil used in gasoline production.

DOE predicted at the time that the Tilt rule would add 1.6 cents to the price of a gallon of gasoline in 1979. Instead, it has added 4 to 6 cents and will cost American motorists $9 billion by the end of 1980.

The Lundberg Survey showed generally steeper prices in the West.