Investigators for the Potomac Electric Power Co. discoverd 2,800 cases of electricity theft in the Washington area last year -- three times the number found during the previous year -- and recovered nearly $800,000 from guilty customers, according to company officers.

The sharp rise in discovered theft caused enough concern at Pepco to make the company abandon its longstanding policy against seeking criminal prosecutions of energy thieves. In a Prince George's County courtroom last week a Suitland man was convicted of stealing $1,300 worth of kilowatts after he found a way to bring electricty into his house without being recorded on the meter. Pepco had pressed charges after investigating the case.

"They cut if off and I just cut it back on," recalled the man, Willie Huntly, 41, an auto body repairman in Hyattsville.". . . The food would spoil if I didn't do it." Huntly said high energy prices -- along with high prices for everything else -- helped motivate him to do it.

Pepco officials emphasized that it is extremely dangerous to tamper with the equipment that supplies electricy to homes.

Larry Barrett, head of Pepco's energy management division, said the increase in discovered thefts last year resulted from the assignment of three full-time investigators to energy theft instead of just one as in 1979.

The implication is that if even more investigators were assigned, more theft would be discovered, but neither Barrett nor anybody else in the electric utility industry is sure how much theft is going on.

"It's substantial, but we can't put a figure on it," said an official of the Edison Electric Institute, an industry trade group.

An economist writing in Public Utilities Fortnightly a year ago estimated that thefts from utility companies nationally may amount to $1.7 billion in electricity and $1.3 billion in natural gas annually.

While the study did not deal with Washington utilities, under its methodology thefts in the Washington and Virginia would total more than $75 million a year, 2 to 4 percent of revenues. That works out to roughly $30 that every customer of Pepco, the Virginia Electric and Power Co. or Washington Gas Light Co. would have to make up.

A Washington Gas Light Co. representative said the company found 60 illegal connections and 63 stolen meters last year -- about the same as the year before -- amounting to a loss of $75,000 that WGL is seeking to recover. She described company antitheft efforts last year as "just about the same" as in 1979.

A Vepco executive, William H. Blackwell Jr., said he thinks the company has less trouble with electricity theft than Pepco because Vepco does not serve large metropolitan areas, although it does serve Northern Virginia and Richmond. Pepco serves the District of Columbia and its Maryland suburbs.

Vepco discovered 970 cases of electricity theft last year and recovered nearly $131,000, about the same as the year before. There was no increase in the company's antitheft apparatus between the two years, but Blackwell said, "I couldn't say doubling or tripling our investigative forces would result in a doubling or tripling of the revenues recovered."

Unlike Pepco, Vepco has long pressed for prosecutions of energy theives. Last year 145 cases were referred to the commonwealth's attorney for prosecution and 67 convictions were obtained, Blackwell said.

At the same time that Pepco had Huntly prosecuted, it tried to prosecute another customer but failed after it turned out last week that it was not the customer but someone else living at the same address who apparently had tampered with the electric equipment.

In that case, the Pepco meter reader became suspicious on a regular visit when he saw that the meter registered less total electricity use than it had a month earlier. He returned an hour later to check again, at which point someone ran out and chased him away.

Pepco depends to a large extent on its full-time meter readers to detect possible theft. The company's 70 meter readers, who wear brown uniforms and earn $7.67 an hour, report anything suspicious to Pepco's investigations branch.

Then special investigators are sent out, and when they confirm a theft the amount stolen is estimated and the customer is pressured to pay. The company collects about 95 percent of by time, Barrett said. He said it was decided to have Huntly prosecuted because his case was of a "repeated and flagrant nature."

Here, according to Barrett, is what happened:

Huntly's house at 2329 Gaylord Dr., Suitland, had been disconnected by Pepco because Huntly had not paid his electric bill. On. Nov. 8, 1979, Pepco meter reader Henry Sites Jr. was sent to the house to make a special check and found evidence of tampering that enabled electricity to flow into the house without its use being metered.

Sites remedied this and diconnected the service so the house again could not receive electricity. More than half a year later, on July 28, 1980, Pepco investigators visited the house and "found the guy had reconnected himself, and so we cut him off again."

This time the company did not wait so long to recheck. A few days later, on Aug. 1, investigators again checked Huntly's house and "he had hooked himself up again. Then we had a Pepco crew go out and disconnect it a fourth time at the pole. At that point, the meter was covered and locked."

Sometime after that, Huntly went to Pepco and paid enough on his account so the company went ahead and pressed charges anyway.

Last Jan. 27 Huntly pleaded guilty on two counts of fraudulently tampering with electrical equipment. Judge Francis A. Borelli placed him on three years' supervised probation and ordered him to repay $1,300 to Pepco for unmetered electricity he had used.

Huntly, interviewed at the Hyattsville auto body shop where he works, said he reconnected his service because he could not afford to pay his bills but needed electricity. He complained about the high cost of energy: "Really, it's too high. What do they do with all the money they take in? . . . . The price of everything is going higher and higher."

Huntly said his daughter was sick and he was faced with, among other things, a big hospital bill. "When it rains, it pours," he said, shaking his head.