A new kind of story is being told by area motorists already hardened to tales from the gas lines: siphoning stories.

One 20-year-old McLean man, Stuart B. Carter, was leaving a friend's house one night last week when he discovered his gas tank had been drained by someone with a siphoning hose.

Annoyed, Carter said he went and siphoned gas from a driver's education vehicle at Langley High School, was caught by police, and spent the night in jail.

In the past few weeks, the reports of gas thefts around the metropolitan area have risen sharply. Montgomery County reported 54 incidents of gas theft last weekend; there were only 41 such incidents in the entire month of May.

Although few arrests are made - because siphoners and other gas thieves are extremely difficult to trace - reports of gas thefts are pouring into all metropolitan area police departments. Prince George's County communications officer Doug Hanegar said yesterday he had received 15 siphoning complaints daily for the last three weeks.

At Thompson's Texaco station at 4000 Georgia Avenue NW, 1,571 gallons of gasoline were stolen from an underground tank last Thursday night although neither the owner nor police have figured out how.

A Texaco station at 1765 New York Avenue NE reported the theft of 47 gallons from its pumps Monday night. Baltimore service station owner Charles Gladstone said that 140 gallons were stolen from him over the weekend. He since has put locks on his storage tanks.

Most area police departments do not have specific statistics on the incidence of siphoning because the crime is lumped together with other thefts of items worth less than $100 in a general category called petty larceny.

Most of the siphoning incidents occur at night and from cars in unattended lots, according to police. But, in recent days, the incidents have grown more serious.

The U-Haul Company of Metro D.C. Inc., which has 66 lots around the metropolitan area, has had gas stolen from 200 of its trucks since the beginning of June, according to office manager Troy Ashton.

"When you rent a truck, it's got to be full of gas," explains Ashton, who adds that each truck holds 30 gallons. "And we don't have any security in many of the lots."

Continually hit are trucks from produce companies along V Street in Northeast Washington. Quality Produce reported 100 gallons stolen over the weekend from eight different trucks, according to a company spokesman. Officials of Douglas Corporation, of 3521 V St. NE, reported to police that one truck was hit at least three separate times over a six-day period, with thieves taking more than 120 gallons.

One effect of the rash of siphoning and gas theft incidents has been a sharp increase in the sale of locking gas caps. Mike Dunne of ARO Automotive, a Wheaton auto supply center, reported yesterday that he is selling 300 locking gas caps a week, up from 20 a week a few months ago.

Judging from the eight arrests made in Montgomery County, many of the siphoners are juveniles, said officer Bruce Blair of the Wheaton district station. "You get a bunch of kids who go joyriding on the weekends and run out of gas," he said.

But not all the thieves are young, and some are downright conscientious. Yesterday morning, one Arlington resident found an envelope on his windshield containing $3 and a note. It read:

"Dear Lady or Sir: In these troubled times of gas shortages I find myself, once an honest law-abiding citizen, engaging in questionable practices. I have purchased exactly three gallons of gasoline from your tank for $1 a gallon.

"I apologize for this incident and I hope soon I will not have to resort to this behavior again."

The note was signed, "Troubled Motorist."