Curtailments of gasoline deliveries by Shell, Texaco and Phillips to most of their 300 stations in the Washington area have forced many station owners to close on Sundays and reduce hours of business.

Mobil, with more than 100 stations in the area, announced yesterday a 13 percent curtailment for March for its dealers here and nationwide.

The Shell, Texaco and Phillips curtailments, also in effect nationwide, range from about 5 to 15 percent of the gasoline normally supplied to dealers.

Dealers and company representatives here say customers are receiving the news calmly and are bringing their business to other service stations where there are no shortages.

The same sources say a "snowball effect" could result if many more of the big companies announce curtailments. They say this would happen because the remaining companies not curtailing supplies to their dealers would be unable to meet the sudden increase in demand from customers switching away from curtailed dealers.

Exxon, the industry giant with 450 stations in the Washington area alone, has not curtailed supplies to dealers. A spokesman in Houston said yesterday that Exxon will announce today whether or not there will be curtailment in March.

"The situation is serious. We're watching it constantly," said another Exxon executive. He said the company -- is drawing down its inventories to meet current gasoline needs.

This is happening at a time of the year when Exxon and the other oil companies are normally building inventories to meet the heavier demands of the coming warm weather driving season.

The Iranian oil cutoff has reduced petroleum deliveries to the United States by an estimated 2 1/2 percent. Other countries are suffering more. Prices have skyrocketed as a result.

A Washington Post survey of 14 gas stations here shows that all but one raised prices since the beginning of the year. Eight have raised prices by 1 to 7 cents a gallon during the past two weeks.

The owner of the station that has not raised prices said he will probably do so by 6 cents a gallon starting tomorrow.

Prices of 80 cents a gallon for premium gasoline were reported at some locations. Premium unleaded gas was selling for 87 cents a gallon in one station.

The Washington area price for number 6 heating oil for apartments, offices, hospitals, schools and federal buildings will jump 12 percent during the next week as a result of Venezuela's decision on Monday to raise the price of much of its oil, according to local industry sources.

This increase will come on top of the nearly 15 percent increase in heating oil prices here during the last four months, according to Leonard P. Steuart II, president of Steuart Petroleum Co. here.

Steuart's the leading supplier of number 6 oil in the Washington area. He said number 6 oil sells for 43 cents a gallon now and will sell for 48 cents a gallon in a week because of the Venezuelan decision.

This is because Steuart, like other suppliers here, buys 90 percent or more of its number 6 oil from Venezuela, Steuart said.

The Venezuelan action does not affect the price of the number 2 home heating oil used in 180,000 Washington area homes because this lighter oil comes from elsewhere, according to Steuart. But supplies of number 2 continue to be tight, he said.

The size of the market for number 6 oil here is thought to be about twice that for number 2 home heating oil.

Potomac Electric Power Co. and Virginia Electric and Power Co. also burn number 6 oil in some of their generating plants. Spokesmen for the companies could not estimate the impact of the Venezuelan decision yesterday except to say that price increases would be passed directly through to electric customers via the fuel adjustment clause.

Checks yesterday with nine major oil companies supplying more than 1,300 stations in the Washington area -- most of the stations here -- showed:

Shell (165 stations), Mobil (113), and Phillips (35) have already announced supply curtailments for March.

Texaco (110) has curtailed previously and is expected to continue doing so in March, although there has been no announcement yet.

Amoco (174) will "probably curtail in March," a spokesman said. It had no curtailments before.

Cities Service (32), Gulf (150) and Sunoco (110) have not yet had curtailments, and spokesmen indicated these companies have no immediate plans to do so.

Exxon (450) will announce today. It has had no curtailments yet.

Shell's mid-Atlantic region manager, Donald R. Healy, said that Shell dealers here will receive 10 to 15 percent less gasoline than they could sell.

He said a similar curtailment in January meant that half of Shell's 165 stations here had to close on Sundays or curtail their hours of operation.

Because of the way federal rules allocate gas supplies during a shortage such as this, not all Shell stations were affected -- or will be during March.

Those who will be curtailed are those who are now selling more gas than they were during a "base period" in the past.

Here's how it works:

Ralph M. Presutti runs a busy and prospering Shell station at the bustling intersection of Allentown Road and Old Branch Avenue in Prince George's County.

In the past decade he has built it from a small station that pumped 35,000 gallons a month to one that pumps hundreds of thousands of gallons a month.

In March of 1978, Presutti pumped 225,146 gallons. Since that is his "base period" under the federal rules, and since Shell has announced a 95 percent allocation for March, Presutti will be supplied with 95 percent of that amount to sell this March.

That is a cut of more than 11,000 gallons, but business has grown during the past year, and Presutti thinks he could sell 255,000 gallons this March if he had all the supplies he wanted.

So the total shortage in his supplies will be roughly 41,000 gallons, he estimates. At an average profit margin of 7 1/2 cents a gallon, Presutti says he could lose as much as $3,075 this March alone.

To prevent that, he said, he must continue to curtail hours so he won't have to pay his employes as much. And he will have to raise prices.

He has already done that, much to his dissatisfaction. He built his business, he said, by underselling the Exxon station across the street. Now the Exxon station -- with its plentiful supplies -- is underselling him by a penny.

Presutti's customers, finding him closed after 6 p.m. and on Sundays, have begun going elsewhere -- many of them across the street to the Exxon.

"Customers are very concerned," Presutti said. "They're not really worried about the price all that much, because they know prices are going up.

"But their real concern is availability. They don't want to go back into the lines about it. I'm already getting my good customers saying, 'Boy, you gotta take care of me, Ralph.' I tell them I'll do the best I can."