Herman and Kia Regusters were sitting back-to-back in their boat on a quiet African lake when, they said yesterday, a dark gray shape from prehistory reared out of the water.

"I saw a long, serpent-like head and neck rise 1 1/2 to 2 meters out of the water," said Kia Regusters, who had come with her husband to remote Lake Tele in search of the world's last surviving dinosaur. "The head moved from side to side . . . my first reaction was that it was very large and very close and I was quite startled."

The reaction from 50 to 60 journalists gathered at the Museum of Science and Industry here was somewhat different when they learned the Regusters had no pictures with them to prove their claim. Despite what Herman Regusters described as several sightings of the creature by all 23 members of their expedition, that one five-second appearance near their boat turned out to be their only chance for a photo, and he said his wife might have blown it.

"It took me a while to snap the picture," said Kia Regusters, a 34-year-old psychologist who was holding an Olympus camera equipped with a zoom lens and Kodachrome 64 film. Her husband, a 48-year-old aerospace engineer working with the Jet Propulsion Laboratory, recalled saying, "Why did I bother to bring her along if she was going to freeze up when we saw something important."

The crucial photograph, if his wife's camera caught anything at all, was still being processed yesterday, along with hundreds of other photos taken in the area of the lake in the northwestern part of Congo. Despite increasingly testy questions from the assembled reporters, all Regusters would say was the photos would be ready "soon."

"We may end up having absolutely no proof," Regusters said, after fielding several skeptical question that noted another recent expedition to the area had come up empty. "But we are positive that the creature exists at the lake."

The expedition tape recorded what appeared to be trumpeting roars by the beast, which resembles in some accounts the brontosaurus, thought to have been extinct for 65 million years. But the tape "doesn't sound like anything at all" unless you know what to listen for, said John Sack, author of "M" and other books, who did not accompany the expedition but has served as its spokesman.

Regusters, who brought former Cable News Network cameraman Darby Switzer, two Congolese government game and park officials and a Ghanaian wildlife expert with him, said he became interested in the dinosaur hunt after reading a magazine article a year ago about strange creatures reported near Lake Tele. One native account said pygmies had killed two of the creatures and eaten them in 1930.

He said he paid for the expedition with $40,000 from his own and his wife's funds, plus money contributed by colleagues at Pasadena's Jet Propulsion Laboratory. The last 65 kilometers to the lake took them through ankle-high and sometimes waist-high swamps. They were accompanied by 17 local guides and porters. "Had we known how hard it was going to be, we might not have made it," Kia Regusters said.

Within two days of their arrival, Herman Regusters said, many expedition members saw a long neck extending out of the water at about 6:30 a.m. and watched it travel a quarter mile before it resubmerged. Another group later saw what appeared to be the creature's back emerging from the water for about eight minutes, leading to an estimate of a beast the length of two hippopotamuses, even though there were no hippopotamuses in the area. They failed to photograph either sighting because their cameras were not unpacked and later mechanical trouble limited the number of observation groups that could have cameras.

Asked why they did not extend their month-long stay until they got better pictures, Regusters said, "The natives said they were not going to stay at the lake any longer. It's a mystical place to them, they are afraid of it and they only go there to hunt."