A three-man team of intrepid explorers is preparing for an expedition into the uncharted jungles of Africa in search of a dinosaur.

Not a fossil. A dinosaur. A live one.

You laugh, but this is serious business. The last group that went looking for the 10-ton, 40-foot mokele-mbembe -- the name the natives use for the creature -- was a French team in 1978. It never came out.

What the scientists, including Dr. Roy P. Mackal, a microbiologist and tissue expert at the University of Chicago, are looking for is the African Bigfoot, the Loch Ness monster of the jungle.

If is exists, and if it is the brontosaurus the native descriptions make it out to be, it would be the only saurus to survive the mass extinction of dinosaurs 60 million years ago.

"Whether there are dinosaurs or not, we don't know," said Mackal, whose colleagues wonder why he is doing this. "But we're going to check it out. I admit to having some romance in my soul."

About the skepticism of his colleagues, he said, "You have to have a thick skin. . . . If they say it's extremely unlikely, then I'm the first to agree. But it's not impossible. We've got to check out the long shots, because they pay off once in a while."

Over the past two centuries, there have been many reported sightings of the reptile, which the natives say frightens away hippopotami. Recently a crocodile expert working near Lake Tele in the Congo photographed a clawed, 36-inch footprint the natives identified as belonging to the animal.

On a recent African trip, Mackal convinced himself of the worthiness of the expedition when he did a little poll of the natives in the area. He took along pictures of a variety of different animals, including some from that section of Africa and some foreign species like the American black bear, and in the midst of the sample was a picture of a brontosaurus.

He said the natives readily identified all the animals from their region, including the brontosaurus. The black bear and other foreign species they said they had never seen. Mackal said he spoke to half a dozen natives who said they had seen mokelembembe.

The region in which the brownish-gray beast is supposed to live is poorly mapped and virtually unexplored except by the Pygmies who live there. Mackal said that the region has changed very little in the past 70 million years, "So if there is a relic species, this would be a good place for it. . . . It's like a lost world in some ways."

The lost world may have been a reference to a work by Arthur Conan Doyle that depicted a lost piece of real estate covered with prehistoric creatures and rediscovered by a small troop of scientists. The story was made into a movie in 1924 and again in 1960.

The equipment for the expedition will include a vial of antidote for the poison from Pygmy blowdarts. 14 kinds of snakebite medicine, and a Buck Rogers-style receiver that will use satellite signals to tell the explorers their exact position in the jungle to within a few feet.

The three explorers plan to go on foot and by native canoe, with no food except what they can pick, hook or hunt, and will be out of touch with the world for three months.

Herman Regusters, an electronics engineer who is taking leave from the Jet Propulsion Laboratory in California, will lead the party into the jungle with the help of the local missionary, the Rev. Eugene Thomas.

Regusters is in charge of the high-technology end of the mission. He borrowed a receiver that can pick up satellite data and process it with some other information to give the explorers their position within a few yards.

To get pictures of the beast he will bring along half a dozen film and videoptape cameras, including a tape camera that can get bright pictures on the darkest moonless night.

To power all this, he says he assembled a backpack-mounted solar plate that can recharge the battery packs over a period of hours.

The natives say the animal stays mostly in the water, and comes to the shore only in the early morning or at dusk to feed on vegetation. "The natives say they are vegetarians only up to the point that you get in their way," Regusters said."Then they can be ferocious, and there are some reports of natives being killed by them."

The creature may have killed the French explorers, but perhaps nobody will ever know for sure. The French team was simply never heard from again.

According to Regusters, some of the natives can be beastly. Although cannibalism and headhunting are outlawed officially in the Congo, he said some still occurs in the outlying regions where the explorers are headed.

The expedition is being funded out of the pockets of the explorers and with some donations and loaned equipment. The group expects to leave from New York at the end of August.

"It's a better bet than the Loch Ness monster," Regusters said. "I'm convinced so far. . . . Though I suppose I may feel differently when I get there."