Two Exxon stations a quarter of a mile apart in Rockvile offer identical products to the motoring public with one major difference - 6 cents a gallon for regular gasoline.

The Hungerford Drive Exxon charges 93.9 cents a gallon for regular and the Hickman Exxon, four blocks away, charges 87.9 cents.

These prices - neither the highest nor the lowest in the area - are examples of the bewildering array of prices found in a Washington Post survey of 42 gasoline stations in the metropolitan region.

Indeed, the survey shows, now that lines have disappeared in many areas, motorists with the inclination to shop around can save as much as 18 cents a gallon on regular gasoline and 19 cents a gallon on premium.

Translated, this means that the owner of a car with a large gas tank could save as much as $4 by looking around.

Many motorists believe that it's worth paying extra to get a certain brand of gasoline.

"We feel we blend the finest ingredients and make our gasoline to the best specifications," said Bill Adams, a spokesman for Phillips 66.

But there are others who insist that brand names are irrelevant.

"The fact is that all gasoline of the same octane and vapor pressure is identical," said Jack A Blum, counselor for the Independent Gasoline Marketers Council.

Gasoline is interchangable, he said. "The proof of it is that the companies routinely trade products, so the gasoline you get may have come from another company's refinery.

Since the Post survey was taken Wednesday, many station prices have gone up again, but spot checks indicated that although the numbers seem to change from day to day the contradictions remain.

The Post survey found:

Eight Amoco stations featuring seven different prices, ranging from a low of 85.9 cents a gallon for regular at a Southeast Washington station to a high of 94.4 cents in the Northwest section.

A self-service station in Silver Spring charging four cents a gallon more than a nearby full-service station.

A difference of 12 cents a gallon for regular gasoline existing among stations within a 10-block neighborhood in Arlington.

"I'm not surprised," said Victor Rasheed, executive director of the Greater Washington-Maryland Service Station Association Inc. He blamed the price variations on U.S. regulations.

In essence, those regulations require stations to peg their pump prices to what they charged for gasoline during a May 1973 base period. But through the use of a half-dozen variables, stations can add to those base prices.

Both Rockville Exxon stations mentioned earlier are charging the maximum allowed under the federal regulations.

John Hickman Jr. is the son of the manager of Hickman's Exxon, where the price of regular is 6 cents less than at a neighboring station. "That's as high as we can go - any higher and we are in violation," he said.

Herb Hollander, manager of the nearby Hungerford Drive Exxon said, there is "another Exxon station one block farther away and he is one cent less than me.

"I don't think there is a gas station around with the same price as anyone else. It all goes back to 1973 - when price rules started."

One result of the rules, the gasoline station dealers contend, is the jungle of prices that have confronted motorists hunting for gasoline.

The lowest priced gasoline discovered in the Post survey Wednesday cost 79.9 cents at a Scot self-service station in Fairfax. The highest regular cost 97.9 cents a gallon at a Sunoco full-service station in Northwest Washington.

Premium had a wider price spread. The lowest was 83.9 cents a gallon; the highest, $1.03.

Unleaded regular was only 83.9 cents at one station but $1 at another.

The smallest price difference found was for unleaded premium, with a low of 94.9 cents and a high of $1.03.

Those extremes offer a glimpse of what motorists will find - even though actual prices have edged up since the Wednesday survey. Exxon, for example, raised gasoline prices 2.5 cents a gallon yesterday. And Amoco had gone up 3 cents a gallon by the weekend.

Other station managers expect price rises this weekend from their suppliers, as the latest wave of increases gushes through the gasoline sales pipeline.

Even within a small neighborhood, there are large variations in prices.

In North Arlington, the Sunoco at 5501 Lee Hwy. had regular gasoline for 92.9 cents a gallon when it was checked Wednesday. Ten blocks away, the Gulf self-service station at Lee Highway and Glebe Road offered regular for only 80.9 cents a gallon.

The difference: 12 cents for one gallon or $2.40 for a 20-gallon fillup.

Brand difference doesn't account completely for that variation.

Two of the Exxon stations face each other on Connecticut Avenue in Northwest Washington.

The Exxon at 5030 Connecticut Ave. NW on the west side of the street charged 88.8 cents a gallon Friday for full service after the Exxon price increase. The Exxon on the east side, at 5039 Connecticut NW charged 90.4.

Asked to explain the 1.6-cent disparity, an Exxon spokesman said:

"That's easy - 5030 Conn. is a company-operated station and 5039 Conn. is a dealer-run station."

Spokesman William F. Robinson said his company has control over the retail pump price only at its own stations. Those run by dealers, who are independent businessmen even though they sell brand name products, "set their own price - as long as they don't violate federal rules," Robinson said.

Konrad Murrer, general manager of the Exxon station at 5039 Connecticut Ave. charges the legal maximum allowed under federal price rules.

"We have a low allocation there - less than 1,000 gallons a day, so we must charge the maximum," he said.

Station officials said there is one other difference: "We have to pay rent to Exxon; the company-owned station doesn't."

The fine line between dealer-run pumps and company-operated stations illustrates the complexity of the gasoline marketplace in these times of scarce supplies and soaring prices.

Now for the bad news.

In what is sure to produce even more confusion at the gasoline pump, dealers are preparing to go to half gallon pricing.

About 20 stations already have begun this system, a dealers' association official said.

This solves the problem stations have with pumps that will not register more than 99.9 cents a gallon.

Eight of the 42 stations in the Post survey, for example, now have at least one grade of gasoline priced at $1 or more.

Station associations in D.C., Maryland, and Virginia have won approval from government officials to charge by the half-gallon. The Virginia group has decals printed and ready for members.

James W. Heizer, the executive director of the Virginia dealers, said the half-gallon system could be used until stations have their pump components altered for higher-priced gasoline.

"We had a meeting with representatives of various pump manufacturers. . . they said it was physically impossible to meet all demands for component parts immediately," Heizer said.

He predicted that the new pump components, will have a longer life than the ones installed after the Arab embargo five years ago. "At that time, pumps could go only to 49.9 cents a gallon," he said.

The group components now on order, he said, will enable dealers to sell a gallon of gasoline for as much as $9.99. CAPTION: Chart, Weekend Gasoline Guide; The Washington Post; Graph, Gas Prices at Area Stations; The Washington Post