Call him the canine world's Lenny Skutnik. But what does he call himself?

That's the question that has bedeviled Elihu, Andrea and Buffy Leifer of Chevy Chase since Feb. 13. They'd like to thank their benefactor, but they don't know who he is.

It's little wonder under the circumstances, which were as gripping to the Leifers as were those of a different sort that faced Skutnik, the man who dived into the ice-clogged Potomac River to help survivors after the Air Florida crash.

This time, the life that was threatened was Buffy, a 2-year-old golden retriever accompanying Elihu Leifer and his 11-year-old daughter, Andrea, on a Saturday afternoon walk beside the Potomac near Carderock, on the Maryland side.

Suddenly, as dogs will, Buffy decided it would be a good idea to take a frisky romp across the ice that covered the river. She had gotten about 50 feet from shore when the slab on which she was standing went ker-r-r-ack, and Buffy fell in.

Buffy can swim fine, but she couldn't organize herself to put her front paws onto the lip of the remaining ice and pull herself out. Quickly, she began to get tired. She began to sink, once, then twice. Soon it would be the end.

Andrea stood on the river bank, crying in terror. Elihu, of course, was helpless, since he weighed several times as much as the dog and could not have reached her by walking out on the ice without seriously endangering himself.

At just that moment, the mystery man came along.

He was about 20, and he was wearing full hiking gear. Recognizing the problem, he stripped off the gear and sprinted onto the ice. When it cracked, he swam the rest of the way. Corraling the freezing, panicky dog, he towed her back to shore.

But in the commotion, the Leifers didn't get his name. Like the Lone Ranger, he was gone before the Leifers realized it.

How about it, hikers or passersby: Who was that masked man? The Leifers would like to reward him --with a puppy.

It seems that Buffy is celebrating her lease on life by casting reproductively significant glances at Trevor, the Leifers' male golden retriever. This can end in only one way, and the Leifers would like to give a memento to the hiker. Stand up and be counted, Mr. Hero.