Yesterday morning, WMAL-AM (630) became the first AM radio station in the Washington area to broadcast in stereo, according to WMAL president and general manager Andy Ockershausen. There's just one hitch--special equipment is required to decode the stereo signal and that equipment is not yet available to the public.

"Just like FM radio, it requires a special receiver," said WMAL chief engineer J.B. McPherson. He said the broadcasting system used by WMAL was developed by Leonard Kahn, whom McPherson called "the father of AM stereo. He pushed for it since the first glimmering of the idea in the 1950s." McPherson said the AM stereo receivers should be in the stores by the end of this year.

"This is a new dimension in transmission, it's kind of exciting," McPherson said. "It provides a width to the sound. It transmits the ambiance of the pickup location right to the listener."

Why broadcast in stereo if listeners cannot benefit from it? "Why wait?" asked Ockershausen. "This is another first for WMAL."

Said McPherson: "Which came first, the chicken or the egg? As soon as the equipment is ready for the home listener, we'll be there with the programming."

The technological advance "will force manufacturers to raise the quality of AM receivers," said Ockershausen, who estimated the cost to the station at $100,000 to $150,000 above the cost of regular replacement of equipment.

Until the special receivers are available, those who wish to experiment with stereo reception can do so by taking "two similar AM receivers, one tuned ever so slightly lower on the radio dial, the other tuned slightly higher," McPherson said. "The more similar the receivers, the more accurate the stereo sound."

WMAL plans a stereo broadcast of the first Redskins home game, Aug. 27 against the Buffalo Bills. "If it works out, we'll do the rest of the home games," Ockershausen said. "Maybe the 'Skins will do better in stereo."