I'VE ALWAYS wanted to probe new frontiers, but my adventurous spirit usually is overcome by the scent of danger. When I learned that each year a thousand tourists explore the upper reaches of the Amazon in Ecuador's El Oriente province by river boat and dugout canoe--and return safe and happy--I knew that I must do it, too. So I joined a Metropolitan Touring group out of Quito.

El Oriente lies 800 miles east of the capital. It is accessible by either a 14-hour bus or jeep ride over primitive roads, or an hour's flight on a 32-seat Ecuadorean army plane. Picturing the first alternative, our group gladly welcomed the second.

The Amazon Basin, almost the size of the United States, is the world's largest rain forest, recording an annual rainfall of about 120 inches. There are few roads, and the widely scattered small settlements give the appearance of enduring extreme isolation. For all that, the discovery of oil a little over a decade ago, and construction of the Transandean Pipeline in 1972, have stirred fears that "progress" may yet spell the demise of one of the few natural regions remaining in the world today. Largely for this reason, El Oriente province, containing Ecuador's share of the Amazon Basin, enjoys the protection of the country's department of agriculture.

When Francisco de Orellana explored this region in 1540, he was attacked by Indians, whom he mistook for the legendary Amazons of Greek mythology, and he discovered a mighty river, which he thereupon named the Amazon. Reassured we had nothing to fear from those Indians we would meet on our trip of exploration, we concentrated on getting acquainted with our new surroundings.

The army plane dropped us off at the small, sleepy river port of Coca, at the junction of the Coca and Napo Rivers, tributaries of the upper Amazon. From there we went by truck to a motorized dugout canoe, capacity 20 passengers, which transferred our group of 15 to the Orellana, our home for the next few days on the Napo.

The Orellana, the only one of its kind anywhere, we were told, is a flatbottomed, triple-decked "flotel" accommodating 54 passengers plus a crew of 20. Each cabin holds from two to four guests and provides a private bathroom with shower. There are a spacious dining room, a small bar, a pleasant sundeck, and a store dispensing such necessities as suntan lotion, insect repellent, rain gear and the inevitable T-shirts and picture postcards. These trips are offered year-round (high season runs from January through March, and July and August) and take place if there are at least two participants.

About eight years ago, when the Orellana was assembled on three pontoons on the river, there already were a few rough roads in the Coca area. They weren't good enough, though, and it was necessary to fly all the parts in from Quito. In most cases, the small settlements and cattle farms in El Oriente still are supplied by dugout canoe.

Though the flotel traveled only about 50 miles during our entire jungle trip, we made numerous river excursions by dugout, the same type used by the natives of the area, and boosted our overall mileage on hikes through the jungle. We wore heavy rubber boots for protection from mud and ground cover, and rough-and-ready outer clothing and headgear to contend with vines, insects, occasional tropical showers, and equally tropical sun.

No question, our land travels were not always easy going. Nor were the hours I had thought to laze aboard the dugout canoe wholly without incident. Late one afternoon, proceeding in the usual carefree manner on our return to the flotel, an unusual torrential rainstorm struck our open craft, soaking us for several hours until, enveloped by fog and deepening darkness, we finally reached our floating home. Fortunately, we were in the hands of two capable crewmen, and our combined camaraderie kept our spirits high if not dry through it all.

But that was a small price to pay for unusual experiences: Exchanging greetings with natives passing in their own dugouts laden with cattle and supplies; marveling at the brilliantly hued birds and butterflies that abound in that lush environment; sampling hearts of palm cut fresh from the tree; smelling the pungent scent of garlic bark, and watching fascinated as an army of leafcutter ants crossed our jungle path.

We also saw "woolly monkeys," South America's largest, and the huge turtles of Lake Taracoa sunning along its banks. We even tried our hand at piranha fishing.

At Lake Limoncocha, renowned for its concentration of over 400 species of birds, we were introduced to such exotics as the hoatzin, anhinga, and cara-cara. It was here, too, that our naturalist-guide Adonis, better known as "Don," assured us that local piranha were not aggressive. Those of us sufficiently convinced by his words cautiously took to the warm lake waters for a pleasant, if somewhat hurried, swim.

Our longer trips in the canoes offered glimpses into the lives of the settlers, whose thatch-roofed huts marked the location of jungle communities and cattle farms. And always, children waving and shouting to us from the shore as we glided by.

Our dugouts on the Napo River were outboard-motor driven, but other boats (paddle-powered to protect the water life) served us on the lake. At such times, group members volunteered to help with the paddles to lighten the crew's chore. Noontime meals were either box lunches or cookouts. All our meals were substantial, tastily prepared, and far more varied than I had dared expect.

The Orellana and the dugouts are under the supervision of the Ecuadorean navy, and there is radio communication with Quito. Since the flotel is relatively close to the airport at Coca, medical enmergencies can be handled with reasonable speed.

"It's an uncommon, an unusual experience, but it can be enjoyed only by those who are ready for it," says Luis Maldonado, tourism manager of Metropolitan Touring, whose firm operates the Orellana jungle trips. New programs are being planned, with tours designed expressly for specialized interests such as geologists, bird watchers, flower lovers, and nature photographers.