Gasoline prices, which have plunged as much as 31 cents per gallon this year in the Washington area, have started to inch upward.

In recent days, several major gasoline companies, including Texaco, Mobil and Gulf, have raised the prices they charge area service station dealers. According to a survey conducted Monday by the Greater Washington Maryland Service Station Association, which represents dealers in the District and Maryland, area stations were hit with the first increases in four months.

"The last survey, everybody was showing anywhere from 3-cent to 7-cent decreases in prices," according to Michael De Santo, government affairs director for the association. "This is the first time we've noted price increases since the downward spiraling began."

Some analysts and oil company officials say traditional adjustments that take advantage of high summertime demand for gasoline are part of the reason for the increases. In addition, oil companies have cut back production in an effort to deal with the glut of cheap oil, lowering the supply of gasoline. These factors are beginning to force prices at the gas pump upward nationwide, according to the analysts, and the levels may not fall again.

"Right now, the prices are going up," said Vic Rasheed, executive director of the Service Station Dealers Association of America, a trade group. "I think happy days are over . . . . The dollar sign [per gallon] is still waiting to be put back up."

Steuart Service Center owner Stanley Parker raised the cash price he charges for regular leaded gasoline by a penny yesterday, his first price increase after months of sliding costs.

"I had to go up on regular this morning," Parker said yesterday from his station in Oxon Hill, Md. He attributed the higher price to increases in the wholesale price he must pay his supplier for the fuel. "They raised the price to me Friday and they raised it again yesterday," he said.

Locally, industry analysts say they are not surprised at the increases, and characterized them as attempts to take advantage of consumers who drive more as the weather warms.

"Traditionally gas prices go up at Memorial Day and continue to rise until the Fourth of July and stay there until Labor Day," according to Mary Anne Reynolds, a spokesman for the Potomac chapter of the American Automobile Association.

A spokesman for Shell Oil said that wholesale increases were the result of high demand and lowered inventories. "Put those two together and it's going to push the price up," the spokesman said.

The higher wholesale prices will mean higher prices at the pump as dealers start passing the increases on to motorists, according to De Santo and many dealers in the Washington area. At an unbranded convenience station in Fauquier County, unleaded gasoline has jumped 5 cents in the past week.

At the Yorktowne Shell in Fairfax County, dealer Jeffrey Mercer said he will hold his prices for unleaded gasoline at 81 cents although his wholesale costs rose this week. But he anticipates higher prices, too: "If they go up again, I'm gonna go up," he said.

Some analysts say that while prices may continue to climb, dramatic increases that would return them to 1985 levels are not expected.

Dan Lundberg, publisher of a national newsletter on energy prices, said gasoline prices around the nation have stabilized as the gap between cheaper crude oil and pump prices has narrowed. Pump prices initially fell slowly and then dramatically because of the time it takes the cheaper oil to work its way through the system, according to experts.

Local prices have been relatively stable in the past few weeks. A survey of 25 gasoline stations conducted this week by The Washington Post showed prices did not drop as rapidly in the past month as they dropped earlier this year when costs fell as much as 10 cents a gallon in one week.

The average cash price of a gallon of unleaded gasoline at self-service pumps in the Washington area dropped 8.3 percent from the average of 95 cents recorded in March by a Washington Post survey of the same stations, to 87 cents in April. A survey of the same stations showed that prices had tumbled 15 percent in March from February levels when the average price for unleaded was $1.12. Some station owners said yesterday they had not cut their prices in two weeks.

According to the survey, prices in the District, where taxes are higher and there are fewer stations to compete against each other, were again higher than in Northern Virginia and Maryland. Some service stations on Capitol Hill and Georgetown this week charged from 99 cents to as much as $1.34 per gallon for unleaded gasoline, well above the District average of 91 cents. The average price in Maryland and Virginia was 85 cents per gallon.