Gasoline prices, which have been dropping steadily for months in the Washington area, will dip below the $1-a-gallon mark here shortly, the area's leading dealer official said yesterday.

Victor Rasheed, executive director of the Greater Washington-Maryland Service Station Association Inc., said that "dollar-a-gallon gasoline will become common here within the next month," largely because of lower wholesale costs and intense competition among dealers.

The same market pressures have already forced the price at one independent station in Baltimore down to 99.9 cents a gallon, Rasheed said.

A spot survey of 100 local service stations in the Washington area yesterday found that the price of regular leaded gasoline has fallen to a low of $1.059 a gallon at self-service pumps--down 12 cents from December. The price was posted at College Park Texaco at 8900 Baltimore Ave. in College Park and did not apply to credit-card users, who pay 10 cents a gallon more. Unleaded regular costs $1.109 a gallon at the station.

Similar price cuts here and elsewhere in the nation reflect the present glut in oil supplies--a glut that prompted the OPEC cartel to announce new limits on production this past weekend in Vienna. The OPEC nations hope that their action will stabilize prices and prevent further price reductions.

In the meantime, the oversupply of gasoline, the use of more fuel-efficient automobiles and the intense competition among individual stations has helped dampen inflation and hold down the cost of living. In February, gasoline prices measured in the U.S. Consumer Price Index fell 2.3 percent, the government announced yesterday, a decline that slowed the rate of inflation to a near standstill of 0.2 percent.

Oil company officials are unwilling to say how much longer prices will continue to drop before hitting bottom. But a representative for one major company said that the present trend could continue through the summer. "The price decline should stop by Labor Day," he said. At that point the price is expected to stabilize, he said.

In the Washington area, motorists will find that gasoline generally costs the least in Maryland and the most in the District of Columbia, according toa survey conducted by The Washington Post, with Virginia prices somewhere in the middle.

That pattern is largely the result of the variation in gasoline taxes levied by the three jurisdictions. The District of Columbia imposes a tax of 13 cents a gallon on gasoline, and Maryland, 9 cents a gallon. Virginia has a statewide tax of 11 cents a gallon and a special Northern Virginia 2 percent tax.

Maryland officials contend that there is another significant reason why their gasoline prices are the lowest in the area. "The oil companies can't own and operate stations in Maryland," said Marvin Bond, a spokesman for the Maryland Comptroller's Office. According to Bond, a Maryland lawimplemented in 1979 preventing oil companies from operating their own stations "provides for more actors" and the resulting competition has kept prices low.

Maryland may lose some of that price advantage, however, if gasoline taxes are increased in keeping with legislation pending in the General Assembly. One measure would raise the tax by two cents a gallon this summer and by an additional 2.5 cents a gallon in 1983.

In the Post gasoline survey, the lowest Maryland price was three cents under the lowest Virginia price and five cents below the lowest District price. College Park Texaco was selling regular leaded self-service gasoline for $1.059 a gallon compared with $1.089 a gallon at the Digas station, 2920 S. Gate Dr., Alexandria, and $1.108 a gallon at Citadel Gas, Kalorama Road and Champlain Street NW.

Similar differences were found in prices for unleaded gasoline.

But the survey also turned up examples of stations charging significantly higher prices for full-service gasoline. At the Van Ness Texaco in Northwest Washington, the cash price for self-service regular leaded was $1.159 a gallon. But the station's cash price for full-service regular leaded was $1.599 a gallon--a difference of 44 cents a gallon.

Charging gasoline on credit cards also can run up the cost of gasoline.

Pumps designated for credit-card use only at the College Park Texaco, for example, are set to charge 10 cents a gallon more than the cash pumps. And if a motorist mistakenly fills his car from the credit-card pump, he is charged the higher price even if he prefers to pay cash.

One other marketing practice that has puzzled some motorists is the linking of the gasoline price with the offer of a carwash.

At the Brookland Gulf Service, 1000 Michigan Ave. NE, a large sign declares that regular gasoline costs 99.9 cents a gallon. In smaller letters, the sign says the 99-cent price is available with a carwash. The pump charges the motorist $1.099 a gallon for regular gasoline. Then the station offers the motorist a free carwash that operator Jim Hickerson says is worth $1.50.

If the motorist buys 20 gallons of gasoline at $1.099 a gallon, he pays $21.98. He then receives a carwash token worth $1.50 and a 50-cent rebate, Hickerson said. That translates to a price of 99.9 cents a gallon for gasoline, according to Hickerson.Also contributing to this story were special correspondents Frank Gaffney, Vince Sedmak and Darcy Trick.