Until a suspect was arrested Friday, the police said, he was known as the most brilliant swindler in the world of pedestrian products.

And although the army of detectives on his trail in recent months had never seen his face, they knew him by the two voices he used - one of a Texan, the other of a New Yorker whose talk was dotted with Yiddish.

''This guy was very different from anything we had ever encountered,'' said Lieut. John E. Kelly, the commanding officer of the special frauds squad of the New York City Police Department, which at times had assigned as many as 25 detectives, 15 vehicles and a helicopter to the light bulb investigation.

''He was very, very cautious,'' Lieutenant Kelly said. ''He had a tremendous amount of discipline. He ran complex operations all around the country and he seemed to be working alone.''

On Friday afternoon, the police arrested a man they identified as Elliot Keith Offen, 35 years old, at a telephone booth at the corner of 58th Street and Seventh Avenue, where they said he was attempting to consummate one of dozens of illegal deals he had conducted in recent years. The deals, Lieutenant Kelly said, had earned Mr. Offen more than $15 million.

Mr. Offen, according to charges filed against him, would convince manufacturers of such products as light bulbs, tape, sunglasses or luggage to provide large shipments to him on consignment. He would represent himself as the head of a legitimate company in their industry, and ask for 30 days to pay for the goods. He would quickly sell the products to an unsuspecting buyer, and then disappear before the manufacturer could find him.

His operation involved the use of almost a dozen telephone answering services around the country and relationships with more than 50 shippers and warehouse companies from Little Rock, Ark., to New York City.