Our ship was one of many crowding the harbor. Beyond it was a stretch of water so wide that in the dark it seemed more a sea than a river. Where the black sky and black water met, the moon was a giant slice of orange papaya with its ends upturned, about to slip into the Rio Negro.

Tomorrow, a few miles downstream, we would be on the Amazon, known from Manaus to the border of Peru as the Rio Solimoes.We were still in our northern clothes and the sultry night air wrapped around us like an unwelcome blanket. Mosquitoes whined past our ears, surveying the unblemished skin on the fresh crop of newcomers. I fingered the insect repellent in my bag but waited until morning to spray my arms and legs - not a completely successful counter maneuver.

The sun was searing and unrelenting that first day and almost every day thereafter. I reminded myself that we were in the tropics, 120 miles south of the equator. It was humid, and on a tour of the city in a bus that wasn't air-conditioned, sweat rolled down my forehead and into my eyes, dripped from my chin, plastered clothes to my body. Even my ears sweated.

According to the thermometer on the M.S. Polaris, the temperature was in the mid-80s, but because of the humidity - even though it was late in the dry season - the air felt much hotter. Guidebooks say the temperature year-round ranges from 75 degrees to the mid-90s and often gets to 100 degrees at midday.

It would have taken too many days to become accustomed to the heat. Instead, we adjusted our schedules to the weather, leaving the ship's cool interior in the morning, late afternoon and sometimes in the evening.

The rain forests we explored were surprising. They weren't the cavernous, dark places I had seen on TV, where trees soar 130-150 feet, where men with chain saws topple them and where wildlife flits through the upper reaches of the remaining trees.

These rain forests, surrounding Manaus and bordering the Amazon River and its channels, look simply like deep woods. There were patches of scrubby, second-growth foliage.

Flood plains, where trees and most foliage had been swept away, spread out from other parts of the river. Often, jungles with impenetrable foliage grow to the water's edge. A few with streams emptying into the river's channels allowed us to travel on shallow-draft rafts into their shadowy depths, drinking in the beauty of exotic foliage.

Trailing vines grow both down and up. Trees put out philodendron-like leaves as big as dinner plates. Other trees bear blossoms and fruit at the same time. Still more surrender their identity to the well-named strangler fig. Its diabolical growth starts out discreetly, with small heart-shaped leaves clamped to the trunk of the victim tree like an innocent decoration. Eventually, the tree all but disappears in the grip of the strangler.

Orchids and bromeliads, Spanish moss and lichens are more benign tree decorations.

Bordering the rivers' channels, nature gives sightseers another generous sampling of the forests' largess. Trees and shrubs and water plants bloom with flowers of many colors. Besides the brilliant ones, many have subdued colors.

Flowers' hues are matched by the birds' - bright macaws and parrots of red, blue, yellow and green; yellow caracaras and yellow-billed toucans; red-eyed, chicken-size hoatzins (sounds like "Watson") with rusty brown feathers and a floppy, punky crest.

Hoatzins' lifestyles are as unusual as their looks. They build flat-as-a-pancake nests over water and don't worry much about their hatchlings, who emerge from their eggs knowing how to swim and climb. When predators are near, the chicks drop into the water to escape. When the all-clear sounds, they make their way to a tree trunk and climb back to the nest with the help of tiny claws on both wings. These first claws drop off as soon as young hoatzins learn to fly.

Over the course of two weeks, we sighted dozens of birds - maybe more than would have been visible in the high canopy of the tall-tree tropical rain forest.

We saw tiny squirrel monkeys by the hundreds in trees close to the water, a few howler monkeys, two sloths, an iguana and many caimans along the Amazon and Orinoco river channels. Morpho butterflies added a spectacular accent of iridescent blue. Hundreds of yellow migrating butterflies formed fluttering banners across a river channel.

In a few places, our paths intersected those of leaf cutter ants. We watched them, careful not to interrupt their passage. Each carried a piece of greenery much bigger than their bodies to build underground apartments. A few carried tiny red blossoms, giving their processions a festive air.

The rain forests we saw are not in immediate danger of deforestation now, because the most prized species already have been taken out, said Roger Stone, author of "Dreams of Amazonia" and a senior fellow at World Wildlife Fund who accompanied the Special Expeditions trip between Manaus and Belem.

"We saw particular types of rain forests, and we saw virgin forests minus the high-quality trees that were logged. Much of the best stuff was removed. Now, greater economic value is attached to some species that once were not so special."

Along the river channels, only a few cut-and-burn land parcels signaled that settlers were clearing land for a homestead. Smoke also rose from the customary burning of last year's vegetation, an annual ritual for farmers.

Stone noted that Brazil's president, Fernando Collor de Mello, had appointed an environmentalist to his staff. He has promised to slow the slash-and-burn farming that already has destroyed 200,000 square miles of the 2-million-square-mile rain forest.

"The worst may happen more slowly" was Stone's faintly optimistic prediction.

Stone saw danger in a direction other than farming. Forest trees are being used to fuel smelters in the eastern Amazon basin where iron ore is mined.

"The mine is an important foreign currency earner. The local smelters need convenient fuel and there happens to be all this wood around. The impact of charcoal workers on the forest is devastating. They consume 5, 000 acres of forest in one week. Environmentalists say destruction of the forest must stop now."

The trip included many treasures.

One was the freshwater dolphins that performed frequently near our ship. Evolved from their ocean ancestors, they rose in perfect twosomes from the river, giving us tantalizing glimpses of their backs curving down into the water.

One night, close to the ship, two curious dolphins surfaced for air, giving their locations away by their snorts and splashes. They circled the ship completely at least once.

We saw only mounted and aquarium specimens of piranha - the Amazon's most famous fish - and pirarucu, which can grow to a length of almost 10 feet. When pirarucu are taken, their thick scales are sold for fingernail files and their tongues, equipped with teeth, are used as scrapers.

Our days on and off the Amazon were eventful and peaceful. One of the quiet pleasures was the "wedding of the waters" below Manaus, where the dark waters of the Rio Negro combine with the coffee-and-cream Rio Solimoes to form a wider, creamier Amazon.

With so many tributaries, the river grew ever broader as we neared Belem and the Amazon's mouth. In the middle of the river, the ship passed the beach at Santorem, where hundreds of bathers looked like specks on the sand.

We made stops at villages along the shore. Where we didn't stop, we attracted villagers who were just as interested in us. Dozens of boys and girls and some adults paddled flotillas of dugout canoes as close to the ship as they dared, to catch the waves of the wake. They flashed wide grins at passengers on deck and yelled with pleasure as their little crafts bobbed in the swells.

Like the Mississippi, the Amazon's bottom shifts daily, making navigation difficult. Even with two local river pilots on board, the Polaris got stuck in the silt at least twice.

Close to the mouth of the river, Capt. Tom Danell took a shortcut through a series of furos or channels, dubbed "The Narrows," and they were. One of Danell's trickier maneuvers was to take the 238-foot-long ship through one 120-degree and two 90-degree turns. He made it, with loud blasts on the ship's horn warning any vessels coming the other way.

Along the channels, the numbers of sawmills and lumber yards increased as we neared the Atlantic. They were all busy. Plumes of white smoke rose from the buildings that had a frontier look, similar to false-front buildings of the early American West.

That the sawmills would provide jobs for many people was surely good news. That the wood may have represented another empty grove in a tropical rain forest was not nearly so thrilling.