About 12 percent of the gasoline station pumps examined each year in the Washington area are mechanically deficient, inspectors find, though they report no evidence of systematic efforts to deliberately overcharge consumers.

The rejected pumps, the inspectors say, give either too little or too much gasoline or have other defects.

Washington-area inspections of 14-724 pumps resulted in 1,743 rejections during recent periods. The statistics aren't broken down into categories, but officials say that roughly a third are for pumping too little, a third for pumping too much and a third for other defects.

The overall rejection rate rises to nearly 20 percent when the figures for the entire state of Virginia, with its many stations in isolated areas, are included.

The inspection programs are carried out by weights and measures specialists and vary widely in their intensity from jurisdiction to jurisdiction.

Prince George's County, for example, has a highly regarded program with nine inspectors, while Montgomery County has only two. Such inspectors generally must inspect taxicab meters and supermarket weights in addition to gas pumps.

In the District of Columbia, 10 percent of the pumps inspected in a recent period of about one year were rejected: in Prince George's the figure was 9 percent; in Montgomery County 20 percent; in Fairfax County 20 percent and in Alexandria 25 percent.

Pumps in Arlington are inspected by the state. Figures for the county are included in the statehs overall figures-a 21 percent rejection rate.

The officials who inspect the pumps at about 1,500 Washington-area stations tend to believe that any ripoffs that may occur are not systematic.

"There are a lot of . . . pumps out of calibration but it's in a random pattern," said Richard M. Helfrich, who supervises pump inspections for Montgomery County.

Helfrich said his department is undermanned and the county's 3,750 pumps are not inspected often enough. "It's not the healthiest situation for the consumer, but there don't seem to be active attemps by the [gasoline station] industry to take advantage of the fact that we're not out there," he said.

About 255 of 1,250 pumps inspected in Montgomery during the past year were rejected-20 percent of them. When a pump is rejected, it must be repaired by the dealer or the oil company before it is placed back in use.

Fairfax County's consumer affairs director Ron Mallard said his pump inspection program seeks to protect consumers, "but at the same time it also prevents retail [gasoline dealers] from losing revenues" when deficient pumps are giving away gasoline.

Of the pumps found to be giving too little or too much gas, Mallard said, "I guess the preponderance of the error usually falls to the disadvantage of consumers but not by a large majority. It might be in the neighborhood of 55 to 45 percent. . .

"Quite often these things are inadvertent. A measuring device will over a period of time go out of calibration and it will be unknown in many cases to the station manager."

Mallard and other officials said it is difficult to determine if a short measure of gasoline from a pump results from tampering or from changes due to normal wear and tear, although it is thought that the amount of tampering is small.

Alton C. Morgan. manager of a Sunoco station at 4510 Duke St. in Alexandria, was fined $250 last month after he pleaded guilty to a charge of misrepresenting the price of gasoline.

The fine was imposed after Louis W. Veznina, a city weights and measures inspector, checked the station and was charged $3.90 for five gallons of gasoline selling at 71.9 cents a gallon. The price should have been $3.60 but the pump dials showed the higher total.

A Washington Post reporter accompanied Vezina last Monday as he inspected 17 pumps at two gasoline stations. He rejected four of them, sealing red tags on them to put them out of operation until they could be repaired or replaced.

Vezina, who has been the city's sealer of weights and measures-a title that goes back to Colonial times-for 20 years, whipped out his calculator and checked a sale on a pump in N.P. Olgesby's Shell station at 1333 Quaker Lane.

The pump was charging a penny more than it should for the sale-not enough for a rejection, Vezina said.

Then Vezina got out his pair of 5-gallon, calibrated "prover" cans and tested a pump to see if it was pumping exact measure. He pumped five gallons slowly into one can and another five gallons at full speed into the other.

The pump was accurate within a cubic inch or so. An error of seven cubic inches or less per five gallons is allowable in all local jurisdictions. There are 231 cubic inches in a gallon and 1,155 in five gallons.

Since Vezina had pumped 10 gallons, he could see on the pump dials that the total price, $7.59, was 10 times the unit price of 75.9 cents a gallon without using his calculator.

Before pouring the gas back into the station's underground tanks, Vezina used a chemical to test it for water content. It had none.

But Vezine ended up putting red "Condemned for Repairs" tags on three of the station's six pumps: all three were old-fashioned pumps with dials that could show a maximum sale of only $9.99. After that the dials began at zero again, requiring the purchaser to add two figures to determine the total price.

One pump also had no glass over the dials and another had some figures on the dials that were worn and impossible to read clearly.

Oglesby, the dealer, got on the phone with officials to Shell-which owns the station-to arrange for quick repairs and replacements for the rejected pumps.

Oglesby said he was glad to have Vezina visit because on a previous visit some months ago the inspector had found that three of the station's pumps were giving away gas at the rate of an extra 3/10ths of a cent a gallon to customers.

Donald R. Healy, Shell's mid-Atlantic region manager, said the company is systematically replacing the older pumps in its stations.

He said the station at 1333 Quaker Ln. is "one of our very oldest stations. It's an antiquated, old, old station. I think those gasoline pumps out there are due to be replaced very very shortly." CAPTION: Picture 1, Alexandria weights and measures official Louis Veniza "red tags" a gas pump. By Larry Morris-The Washington Post; Picture 2, Louis Vezina tests accuracy of a gasoline pump in Alexandria. By Larry Morris-The Washington Post; Chart, Deficiencies in Gas Station Pumps, The Washington Post