While the average Washington area motorist is absorbing the brunt of the oil shortage, farmers, fishermen, construction and car rental companies, messenger services and others are not feeling the pinch quite as much.

They are among a vast and growing array of special interests who receive priority allotments of gasoline and diesel fuel.

By the time the 5 percent worldwide oil shortage is made worse by special deliveries to those on the priority lists, it has become a 20-to-25 percent shortage at the gasoline pump where the average Washington motorist waited in line yesterday.

"More and more of our supply is being earmarked to priority users," said Shell senior public affairs representative Michael O'Toole. He said this means that less gasoline is available for Shell's retail outlets, including 165 stations in the Washington area.

But while there were lines here, gasoline supplies in nearby rural areas were plentiful.

"The rural areas of America are getting proportionately more gas than the metropolitan areas, and it's the metropolitan areas that are seeing the big influx of demand," O'Toole said.

He said this was because the complex system of federal priorities primarily is geared to supplying agricultural gasoline and diesel needs through a network of rural middlemen.

William L. Wise, a Cambridge, Md., oil dealer supplied by Shell, said his 200 priority customers - mostly farmers and Chesapeake Bay watermen - are buying up to twice as much fuel from him as they did last year.

These priority customers are entitled to all the gasoline and diesel they want from Wise before any can be sold to his service station customers and other regular customers.

Wise said crabbing on the bay is better this summer than last, which increases the watermen's fuel needs.

But Wise thinks some are cheating, too.

"A farmer or waterman with 14 or 15 people in his family, and they all come home and fill their cars up," he said. "You got people using out of the priority pile that don't belong there. The poor man who suffers the most is the [service station] dealer, and he has to pass it on to the man in the street."

The federal allocation system was created during the 1973-74 Arab oil embargo to distribute scarce supplies in an equitable manner during a fuel shortage. It came into being again early this year when a worldwide oil shortage developed.

The priority system that is part of the allocation system also was used in 1974 and is designed to put most of the burden of a shortage on the average motorist because he is considered better able to cut his fuel consumption than a trucker or a farmer.

But now the oil industry is worried that motorists are being cut back too much and that the priority system is leading to hoarding and blackmarketing.

"Any time you have privileged classes, this is how black markets start," and industry observer said. "Anybody serving a priority user can skim off some of that . . ."

There are two ways to get priority fuel allotments. Farmers and others on the federal priority list may simply go to their supplier and "certify" themselves as priority customers by filling out a form. The supplier must then supply the farmer with all the fuel he wants - before any goes to nonpriority customers.

Federal officials and the oil industry estimate that 5 to 10 percent the nation's gasoline is supplied to priority users by this method, with the amount growing weekly.

An additional 5 percent of the nation's gasoline is "set aside" for state officials to distribute at their discretion for emergency and hardship cases.

The states usually follow the federal priority lists in doing this, but they need not justify their actions to the federal government.

Virginia, Maryland and the District of Columbia administer their set-asides differently.

Virginia and the District give some setaside allotments to service stations, but Maryland does not, claiming that the administrative burden of determining which stations are needy is too great.

Virginia energy chief George Jones has 6 million gallons of gasoline in his setaside each month and has handed it out to farmers, service stations, construction companies, fertilizer companies, bakeries, pulp and wood haulers and a limestone crushing company.

Jones said hundreds of callers are demanding priority allotments, leading to "one hell of an administrative problem."

In the District of Columbia, energy chief Chuck Clinton is parceling out about 400,000 gallons of setaside gasoline a month.

Fannon Petroleum, a Virginia firm, got 8,000 gallons from the District setaside. David Fannon of the firm said the gasoline was passed on to "end users" in the city - taxicab, moving and car rental firms.

"I don't know whether they'd go out of business or not [without the priority allotment]," said Fannon, "but they've got as much hardship as anybody else."

The Warner Corp., a plumbing firm with 120 trucks, also got 8,000 gallons from the District setaside. "It helped, but we're still probably going to run short," said a supervisor at the firm.

The Washington Star got a 7,600-gallon priority allotment for its delivery truck fleet. Without the allotment, a spokesman said, the Star's business would have suffered.

Clinton's office also earmarked priority allotments for a messenger service, the architect of the Capitol, Avis Leasing and the Salvation Army.

When someone receives a priority allotment, it generally means there is less gasoline left in the pool to be distributed to the average motorist.

The Department of Energy keeps expanding the lists of priority users, and oil industry representatives say this adds to the shortage for the average motorist.

DOE increased the state set asides from 3 percent to 5 percent last month, and now the nation's truckers are threatening to block highways unless they receive special fuel allocations.

The federal gasoline priority list ranks privileged users in this order: agriculture (including fishermen), defense, emergency services, energy production, sanitation, telecommunications, passenger transport, cargo freight and mail hauling by truck, aviaiton ground support vehicles, and industrial, commercial, government and social service uses.

Any person or business that can relate his work activities to a priority on the list has a chance of receiving a priority allotment by applying to state or federal officials.

DOE set the diesel priorities on May 10 as agricultural production and trucking of perishable agricultural commodities. On May 25, the list expanded to include surface mass passenger transportation and production of oil and natural gas.

The expansion of the priority lists never became a major factor during the 1973-74 Arab oil embargo because there wasn't time. There was only one month of real stringency at the filling stations - February 1974.

The oil companies have also been asked by President Carter to build up the stocks of home heating oil for next winter. These stocks are sorely depleted and while the companies are building them slowly, company representatives say they may have to cut into gasoline production as the summer wears on in order to build the heating oil stocks more rapidly.

Ed Murphy, director of statistics for the American Petroleum Institute, said that as the oil industry builds its home heating oil inventory, gasoline and crude oil stocks are not being built. In fact, he said, the nation's gasoline stocks are just holding "within a hair's breadth" of what is known as the "minimum operating level" - the quantity of gasoline that always must remain in pipelines and storage tanks so the distribution system itself can function.

Oil industry representatives say the current shortage of gasoline will last all summer and into the fall and winter when heating demands rise. They emphasize that the end is not in sight.

As the shortage continues, the numbers of those clamoring for priority status increases. According to The Lundberg Letter, a petroleum marketing publication, gasoline deliveries in America decreased from 102 percent to 91 percent of last year's deliveries during the period March to June this year.

During the same period, the proportion of deliveries going to priority customers increased from 8 to 14 percent.

An analysis by The Washington Post of statistics provided by the seven companies that supply 1,300 of the Washington area's 1,500 service stations - Amoco, Exxon, Gulf, Mobil, Shell, Sunoco and Texaco - showed that this month the companies plan to supply a total of 90 percent of the gasoline they supplied during June a year ago.

But the analysis shows that service stations in the Washington area will receive only 75 to 80 percent of what they received last June from these companies.

That means that 10 to 15 percent of the supplies coming into this area are now going to priority users, industry officers say.

Of course, some of those priority users would have bought at ordinary stations and now are not doing so because of their priority allotments, the officers say, which may decrease demand somewhat on the stations.

With normal demand for gasoline rising at about 5 percent a year, the shortfall for the average motorist may rise as high as 30 percent, industry officers and observers say.

Here's how Shell figured how much gasoline it could distribute nationally during May, according to O'Toole.

In May 1978, Shell sold 769 million gallons. Its customers would want at least that much a year later, Shell executives figured.Also, they figured that priority allotments and other DOE-ordered allotments would come to 51 million gallons in May.

The total was 820 million gallons - the total the company could be called on to deliver if last year's customers called for 100 percent of what they got last year.

But Shell didn't have that much to sell in May 1979.

So after looking at its curtailed crude oil supply and its obligaiton to build home heating oil stocks, Shell decided it could sell a total of 692 million gallons in May 1979 - considerably short of the 820 million it needed.

Before that 692 million gallons can be parceled out to service stations, jobbers and other outlets, however, Shell had to earmark 38 million gallons of it or 5.5 percent for priority users, and 21 million gallons or 3 percent for the state setasides.

That left 633 million gallons to be distributed under the federal allocation rules - or just 81 percent of what was distributed in May a year earlier.

The 81 percent is known as the "allocation fraction" and service stations and other customers basically receive that cut of what they received last year with some of them receiving a slightly higher amount under the complex allocation rules.

But while regular customers received only about 81 percent of year-ago supplies, Shell planned to distribute the 692 million gallons, or 90 percent of year-ago supplies.

The difference went to the priority customers.

Because company executives has to make these plans conservatively, they ended up actually supplying 730 million gallons to the nations this May - or 95 percent of a year-ago supply, with some of the extra supply, with some of the extra supply going to regular customers and some to priority users.

In Annapolis this week, Maryland Comptroller Louis L. Goldstein raised another spectre-oil middlemen hoarding gasoline while prices rise.

Goldstein advocated new controls over such activity, saying it aggravated the shortage.

He traced in a press release a brokerage transaction showing how 7 million gallons of gasoline was accumulated by a broker or middleman, held in storage for up to 60 days and then sold at a large profit in April.