"YOU DON'T have to worry about the sharks here. The sharks in the Great Barrier Reef are so well fed that they don't bother anyone."

The words were spoken by my diving instructor, Mike, as he strapped a dagger onto his ankle. My skepticism was nearly complete. I was readying myself for my first dive ever, anywhere, and somehow the image of a well-fed shark was only slightly less menacing than that of a shark that was starving.

"Then what's that, uh, knife for?" I asked with genuine interest.

"Oh, fishing line you might get caught in--that sort of thing." Mike busied himself with tanks, masks and fins for a few minutes, then he turned and flashed me a fraternal smile. "You ready to go?"

"Sure."

And suddenly I was. I wanted to be cool about the whole thing. After all, death comes in many guises, and there must be far more ignoble ways of ending things than to become entangled in a ferocious, white 1,500-pound piece of fishing line with jaws strong enough to disembowel a Lincoln Continental. In addition, I was thousands of miles from home and--with only the vaguest idea of what day of the week it was--rapidly succumbing to what seemed to be an Australian rather devil-may-care approach to life. In short, I was ripe for a risk or two, so I decided to plunge ahead and look on the bright side. Fortunately, the bright side was considerable.

It was a brilliant afternoon, cloudless and warm. I was standing on the deck of the Reef Encounter, a boat anchored nine months of the year in the peaceful lagoon of Hook Reef, toward the southern end of the 1,200-mile Great Barrier Reef, about 30 miles off the coast of Queensland. From where I stood, the only interruptions I could see in the rolling blue-green expanse of the Coral Sea were the distant humpbacked outposts of the Whitsunday Islands to the west and, closer to the boat, the mottled brown of the reef itself, the diver's mecca, now seeming to rise out of the sea as the tide retreated from the lagoon.

The previous night was spent aboard the Reef Encounter, an old World War II submarine chaser refitted to accommodate two dozen guests and an eight-member crew. The guests (there were six of us) had dined well on Coral trout and fallen into an easy camaraderie with the crew, who had joined us for the meal. After dinner, some of us climbed to the boat's top deck where, on that moonless night, the stars of the southern sky could be viewed with astonishing clarity and completeness. Silent, deeply enchanting, pointing south to the edge of the world, the Southern Cross cast its spell of incomprehensible longing. I immediately fell under its influence. I was at large on the boundless sea and ready for anything, including all that was strange and wonderful beneath the waves.

Later, we satisfied a more understandable longing by gathering around the boat's tiny bar. Over stubbies (short-necked bottles) of Queensland's own Castlamine XXXX Ale and Australian rum, we spoke with the crew members about the reef and how each of them had come to live on it. The crew, very easygoing and irreverent in all other matters, became serious and fiercely protective when talking about the reef. They had come to it at different times, of course, but in each case they had been answering a call.

Mike, one of two scuba divers aboard, had been born and raised in Brisbane, a large city some distance to the south. About two years before, feeling dissatisfied with metropolitan life, he took a trip up the coast.

"I was driving north on the road that comes in Airlie Beach," he said, referring to the small coastal town slowly emerging into its natural modern role as a jumping-off point for the Whitsunday Islands and the reef, "and I came 'round a curve and the whole thing was laid out before me: the town, the islands, the ocean. I knew, instinctively almost, that I'd found the place I wanted to be. There really isn't any other place like it on earth." Martin, the resident fisherman, had first come to the reef in the late 1960s.

"You don't live on the reef so much as you live with it," he said. "I've been here 15 years, and I still see things that are new to me almost every day."

Martin and the others stressed more than once that, while the reef is a thing of great beauty and immense variety, it is also very fragile--something we should bear in mind when venturing out on it the next day.

There were several different ways of viewing the reef: scuba diving, snorkeling, fishing, riding in a small glass-bottom boat, or reef walking, in which the reef is inspected on foot at low tide. All instruction, equipment and guidance would be supplied by the Reef Encounter.

Somewhere in the midst of our chatter about life at sea, the process of desalinization, American cars, matchbox tricks and distilled spirits, I had quietly made my choice. I took a deep breath and told Mike. He said we'd need an hour or so of instruction in the morning, then have lunch, then dive. I felt obliged to tell him that the closest I'd ever come to scuba diving was watching Lloyd Bridges on the old "Sea Hunt" television show.

"That's okay," Mike said. "You'll be well prepared."

With that, I went below decks to my bunk. The accommodations aboard the Reef Encounter are serviceable but hardly luxurious. The snug cabins, narrow beds and bare comforts elsewhere on the boat are perfectly in keeping with the sense of adventure one wishes to experience on the reef. I climbed into the top bunk, opened my porthole and, lulled by the gentle sea breeze and the rhythm of the water slapping the boat's side, managed a little studying up on the reef before I drifted off.

The Great Barrier Reef is neither a single reef nor, strictly speaking, a barrier. It consists of more than 2,000 individual coral reefs and 71 coral islands, all differing considerably in shape, size and nearness to the mainland. The reefs are created by the steady growth of living coral polyps building upon the limestone skeletons of their ancestors. These polyps, highly colorful, diverse and complex, are animals rather than plants, and they feed, mostly at night, on plankton. Taken as a whole, the reef is by far the largest living thing on earth.

In addition, the reef is home to an abundance of other living things; it throbs with life. This includes a bright treasury of shells, ranging from giant clams to lethal little cones to the aptly named Papal Miter and Articulate Harp. Swaying here and there across the face of the reef are the yellows, greens and blues of an assortment of sea grasses and underwater plants.

And then there are the fish. More than 800 species live on or near the reef: fish in every imaginable shape, color and size; fish that leap, that lurk, that capture flying insects with jets of water; fish with names such as Painted Sweetlips, Convict Surgeonfish, Moorish Idol, Spangled Emperor; millions of fish. Such was the world I would enter the next day.

Following an unbroken sleep of sweet dreams, I awoke, climbed upstairs into the morning sunshine and jumped overboard. After a refreshing swim and breakfast, other guests began dispersing to their chosen pleasures--one went fishing, others bobbed off in the glass-bottom boat.

My blackboard scuba lesson with Mike was short and to the point: Try not to kill yourself. Keep breathing; equalize pressure as you descend by pinching your nose and then forcing air into it; stay near your diving partner. He explained each piece of equipment and its function. I was then deemed ready for my shallow-water lesson.

If there's one thing I observed about Australians it's that they respect the intelligence and ability of the individual. There are few hand-holding instructors in Australia (although in most other popular diving centers certification is a necessity). If you seem reasonably competent and fit, and you want to give scuba diving a go, you go; you don't spend eight weeks sitting at the deep end of the YMCA pool waiting to be certified.

In any case, there was no time for me to worry about what I was getting myself into. After a splendid lunch of poached Red Emperor and salads, we clambered onto a launch and motored through a gap in Hook Reef to the diving ground. I was not fully decked out in scuba equipment. The heft of the tank and the weight belt gave me a sense of purpose, so I squinted as professionally as I could until we were in the water.

After about 20 minutes of precautionary exercises in four feet of water--tossing the breathing device away and then retrieving it, letting the mask fill with water then emptying it--Mike signaled an "okay?" sign with his thumb and index finger. I signaled back that I was ready to go. He then turned and began swimming down into the reef, with me following as if I were on a leash. We were off.

At first I was too wrapped up in what I was doing to notice much about where we were going. The breathing through the regulator was reassuringly easy and natural. I was propelling myself with my legs and feet only; my hands were clasped under my stomach. All was silence, save for the sound of my own breathing. Then gradually, as my confidence grew, the new world opened up before me.

We were swimming through a sort of channel in the reef, with coral walls rising on both sides. The permutations of the coral were almost ludicrously complex. There were purple staghorn formations like clusters of antlers. There were corals like mushrooms and some like furry bedroom slippers. I paused to run a finger across the delicate ridges of an underwater fern. After a while, a wonder at the natural architecture of the reef set in, the sort of silent awe one feels standing before Niagara Falls or peering over the rim of the Grand Canyon. I swam silently and unobtrusively and hoped that the wild prodigality of the reef would not literally take my breath away.

There were the fish to consider as well--everywhere, in every color, swimming singly or in small groups, or in enormous schools. We swam to the end of the channel, which was also the edge of the reef. Beyond and below us lay only the blue-green depth of the ocean. We paused for a moment, and then Mike plunged off the edge. I followed, and almost immediately was lost in a shimmering blizzard of Blue Neons, small fish so brilliantly colored that they do indeed seem electrically charged.

We worked our way down the outer wall of the reef to a depth of about 30 feet. A magnificent Blue-banded Angelfish swam up to my mask, glanced in and continued on. Mike teased a giant clam about the size of a hassock into opening and snapping shut its great jaw. A fiercely territorial brown fish about eight inches long repeatedly darted at us and then retreated, like one of those little guys at bars who always want to fight.

We swam on, pausing here and there as Mike pointed out a sea cucumber, a cave, a particularly beautiful outcropping of coral. After what seemed like hours but was not nearly so long, I checked the meter and found there wasn't much air left in my tank. So we glided smoothly back to the channel, then to the launch.

The afternoon seemed doubly bright and alive with the sounds of wind and waves as I waded out into it. In the distance, a few people from the Reef Encounter were walking on the reef, hunched over, stepping carefully so as not to do damage, but looking as though they were walking on the ocean itself.

Not that it would have surprised me had that been true. At that exhilarating moment, anything seemed possible. The world itself seemed to have grown immeasurably.