Exxon, metropolitan Washington's largest gasoline supplier, yesterday became one of the last of the major oil companies to announce a curtailment of supplies to dealers in the area and nationwide.

The announcement brings to 1,250 the number of Washington area stations whose suppliers have curtailed deliveries, but area dealers said yesterday that customers are not being turned away from the pumps.

However, they said the curtailments will mean higher prices, shorter hours and more Sunday closings -- especially toward the end of the month.

Exxon has 450 stations in the area and claims 20 percent of the local gasoline market. There are thought to be between 1,500 and 2,000 outlets in the area.

Gulf, with 150 area stations, is the only major company that is still supplying dealers with all the gasoline they can sell. Over the past weeks and months, one major company after another had announced curtailments. So far, at least 11 companies have cut back supplies to their dealers.

"Our supplies are tight, we're watching the situation daily," a Gulf spokesman said yesterday.

Some area Exxon dealers said yesterday that they will have as much as 15 percent less gas to sell in March than they could sell if supplies were plentiful.

An Exxon spokesman in Houston said yesterday that the curtailment is due to reduced supplies of crude oil following political turmoil in Iran and cutoff of its oil exports.

The company urged customers to "practice conservation."

Another Exxon spokesman said, "The whole purpose of this is to try to protect our summer gasoline stocks." Prior to yesterday's announcement, Exxon had been reducing inventories to meet current demand, rather than building them in preparation for the summer driving season.

The company has experienced a higher than normal growth in demand because federal price controls have kept Exxon's prices 2 to 5 cents a gallon below the prices of its competitors at the wholesale level, according to industry sources.

"It's going to have a hell of an impact at the end of the month," Exxon dealer James Lowery said of yesterday's announcement. "I'll definitely be (closing) down Sundays, no question in my mind about that."

Lowery, who runs a station on Georgia Avenue in Silver Spring, also said he will have to raise prices "to offset the lack of gasoline that (I) can sell."

Lowery said his station pumps about 100,000 gallons a month and that he could sell 15 to 20 percent more gas this March than he did the same month a year ago. But the new Exxon curtailment will limit him to the same amount he pumped a year ago.

Making things worse, Lowery said, he began the month of March with his underground storage tanks "bone dry," whereas normally he begins a month with about 12,000 gallons in his tanks.

This happened because a tank truck delivery of gasoline to Lowery's station was delayed by snow in late February. The delivery was made after March 1, and as a result will be counted as part of Lowery's now limited March supply rather than his February supply.

George A. Desmarais, who runs an Exxon station in Prince George's County, said the curtailment will cut his March sales by 10 percent -- the amount he could sell this year in excess of what he sold last year.

Desmarais said customers yesterday hadn't yet heard about Exxon's curtailment, but have already been concerned about shortages.

"They say, 'Don't forget me when that day (of cutbacks) comes,' that sort of thing. I say, 'Sure thing.'"