The cabbie must have seen Steffan Akerman coming a hundred miles away.

A 35-year-old Swedish businessman, Akerman landed at National Airport on a recent Friday night after a half-day journey from Amsterdam.

He was tired and wrinkled from so many airplane seats. He also speaks English with an accent. So when Akermann hailed a Yellow Cab and asked to be taken to an address in Cleveland Park, where he was staying with friends, he looked like just the sort of customer who wouldn't recognize, or complain about, an overcharge.

Indeed, Akerman paid the cabbie $12 for a trip that should have cost $7.85. He asked for a receipt so he could claim the trip on his expense account. The cabbie obliged, but, slick to the end, he "failed" to write his cab number on the slip. He was long gone, and untraceable, by the time Cornelia Hollander, Akerman's hostess, clued her guest in on what had happened.

Only a four-dollar ripoff, you say? Not from Loe Harmon's chair.

Harmon is the rate supervisor for the Washington Metropolitan Area Transit Commission. Although he is not a policeman and does not have subpoena power, Harmon can strip individual cabbies of the right to operate between the District and either Maryland or Virginia. He can also refer D.C. drivers to the city hack inspector for a hearing.

Harmon asserts, however, that simply tracing a driver who is involved in a suspected overcharge and asking him about it "will mean that the customer gets his money back 90 percent of the time.

"Most of my complaints are airport runs, just like the Akerman situation," said Harmon. "I average about one complaint like that a day. It runs to thousands of dollars. It's no small problem, I can assure you."

Harmon has this advice for passengers who hail cabs at Dulles or National Airports, particularly foreigners or obvious out-of-towners:

"First, ask for a receipt every time you ride. D.C. drivers, who are most of the problem, are required to keep a carbon of the receipt they give you for 90 days. That'll at least give me a way to start if there's a problem.

"Second, don't trust the receipt. After you get out, personally observe the cab number and the company. I can't tell you how many dishonest drivers will write down the wrong cab number. If you check the number yourself, it gives me a little more than the handwriting to go on."

Harmon welcomes complaints and questions from the public, as long as they relate to interjurisdictional trips, the only kind of cab ripoff over which he has any control. Harmon's phone number is 331-1671. His address is 1625 I St. NW, Room 316, Washington, D.C., 20006.