UFO buffs in the Washington area became quite excited about the sighting Wednesday night of an unidentified flying object resembling a blimp with blinking lights moving through the sky over the city like a "giant jellyfish."

A number of Prince George's County residents and a Maryland state police officer reported seeing the UFO. And a story in yesterday's editions of The Washington Post about the sightings drew numerous phone calls to The Post, Maryland state police and Andrews Air Force Base in Camp Springs.

But it turned out that the expert on this particular UFO was Nadine Brown. The UFO, she told a reporter yesterday, was actually an airplane she owns with her husband that flashes advertising on the bottom of its wings with blinking lights.

"When I saw the article in the newspaper I really laughed - we are the culprits!" said Mrs. Brown, who giggled as she explained that her husband had been flying the advertising plane in the skies here since March.

The reason the Cessna 150 equipped with 315 blinking light bulbs is so often mistaken for a blimp, "flying jelly fish" or mysterious UFO is because it flies at a slow speed of only 45 to 55 m.p.h., Mrs. Brown said.

In addition, she said, "you can see it from a long ways away, but you can not read the message unless you are a quarter of a mile on each side of it." So, from a distance, "you see a jelly fish sort of thing.

The plane is available for an hour each evening Monday through Saturday, according to Mrs. Brown, to flash advertising messages from the bottom of its wings. On Sundays, she said, it flashes passages from the Bible for about two, hours shortly after dusk.

The couple got involved in flying, according to Mrs. Brown, "because we wanted to do something together since our three children had left home and we were like ohter couples who find themselves strangers at this time."

They probably would still have not gotten a plane if they had not stumbled upon the idea of using an advertising plane as a tax write-off, Mrs. Brown said. The plane was advertising a local car dealer's name, location and emblem Wednesday night at approximately 9:45 p.m. when the UFO sightings began.