IF YOU DON'T MIND HIPPOS NIPPING AT YOUR RAFT, TAKE A TRIP WITH SOBEK

Two rafting magnates from Calaveras County, Calif., Richard Bangs and John Yost, now orchestrate adventures from the white waters of Kashmir-Ladakh in India to the ice fields of the North Pole, but when they first began they couldn't even get out of the woods in the Washington, D.C. suburbs. Bangs, 31, and Yost, 29, have been buddies since they were teen-agers in Bethesda, Md. and started a high school rafting club that didn't have rafts. They figured they'd copy Huck Finn by building their own craft and launching it into the heady waters of the Potomac, but all they launched was a very tall tale. They were picking up logs for the raft when a forest ranger stopped them; they were so chagrined that they hid out for a couple of days and made up a story about how they had shot the Potomac rapids. It was such a good yarn that it made the school paper. Now they don't have to invent stories. Their adventures are so real that they can rent them out.

Bangs and Yost run Sobek Expeditions of Angels Camp, Calif., the only global adventure-travel company that specializes in rafting. They formed Sobek in 1973 before Bangs set off on pioneering runs down the previously unnavigated Awash and Omo rivers in Ethiopia, which were once tributaries of the White Nile but have since changed course. (Sobek is the crocodile god of the Nile.) "We were just a couple of aggressive young guys with no resources at all, who didn't want to do real work," says Bangs. "It really tested our ingenuity."

By posing as a wing-forward on a British rugby team, Bangs was able to fly cut-rate on a charter to Ethiopia. Yost, whose father was deputy chief of the U.S. Mission in Ethiopia, flew over for free as a dependent. They arranged to send their rafting gear with the mission's military mail, and fund the trip in part with grants from the Smithsonian and what is now Addis Ababa University to study the insects and freshwater mollusks of the Omo and Awash. But what they really wanted to study was the water. Bangs spent three months consulting with local electric companies about currents and rummaging through dark, dank libraries for charts and explorers' accounts.

Bangs describes his initial 30-day voyage down the Omo in Victorian prose that sounds as if it were written by Stanley shortly before he found Dr. Livingstone: "Imagine for a moment a river so mighty that it has carved out a 4,000-foot canyon of immense proportions, beauty and complexity, yet almost totally unknown except to a handful of the world's cartographers. Imagine, too, this river flowing for countless eons and yet so isolated from human affairs as to exist completely outside human history. Imagine all this and then give the river a name. Call it the Omo."

For $2,475 plus airfare, Bangs and Yost now send passengers down the Omo, in addition to two dozen other more or less exotic rivers on six continents. Sobek's worldwide network of guides and river rats takes rafters in inflatable rafts down the turbulent Bio-Bio in Chile (15 days for $1,820), Alaska's glacier-fed Tatshenshini (12 days, $1,390) and the primitive Watut in New Guinea (six days, $775).

For those who don't cotton to rafting, Sobek offers, among other things, bird-watching tours of the Andes and Amazon (26 days, $1,710), camel safaris in the Australian outback (19 days, $1,740) and treks with Sherpas on the slopes of the Himalayas (30 days, $1,485).

But rafting is still Sobek's primary product, and it's hardly a tame one. Hippos and crocodiles have a habit of nipping at the inflatable boats as they float down the Omo, and last June all 16 members of an expedition on the Coruh River in Turkey were arrested for rafting without a permit. One of Sobek's original partners, Lew Greenwald, drowned in East Africa seven years ago when his raft capsized. He was buried on the bank of the Blue Nile. Greenwald's death took off some of his partners' wild edge. Bangs brooded about withdrawing from the rafting business altogether. But Yost talked him out of it. "The experience humbled us," says Yost. "We realized that we were challenging a river, and that there were penalties involved."

There are still challenges unmet and rivers unconquered. Bangs and Yost are looking at the great rivers of China, the Yellow and the Yangtze. "Our hope," Bangs says, "is to become the adventure-travel organizers of the world."