The grizzly reared up on its hind legs. It swung its head to the side and let out a blood-curdling bellow. The bear was on the opposite bank of the river about 150 yards from us. Full-grown, seven to eight feet tall, probably 800 pounds. And angry! The six of us stood transfixed. The roars reverberated between the narrow walls of the canyon. Then the bear dropped down on all fours, still bellowing, and loped along the sand bar.

Carl dove into the tent for his shotgun. The rest of us hurled wood onto the dying campfire and grabbed for noisemakers -- pots, pans and spoons. Fear knotted my stomach. Bears were supposed to be afraid of humans. To run from fires and noise. In all my trips to Alaska, the bears I had seen always turned and ran. But this grizzly plunged into the river, swimming directly toward us.

Suddenly we realized the reason for the bear's fury: We were in its hunting grounds. We had not planned to be. In fact, we were congratulating ourselves that very morning on how well we had planned this three-week wilderness trip on the Porcupine River from Old Crow, Yukon Territory, to Fort Yukon, Alaska. A 360-mile paddle, all above the Arctic Circle. This was our fourth day out and we were getting the hang of our two canoes and two kayaks, feeling pretty good about how our old bones were holding up to paddling, packing gear and sleeping on gravel bars. We were, after all, sedentary creatures stuck behind desks most of the year. Moreover, we were all 55 or over and didn't even jog.

But age has its assets. Our combined experience was considerable. The six of us were two former U.S. ambassadors (Jane Coon, who had just completed her assignment to Bangladesh, and her husband, Carl, who had finished his in Nepal); Bir Bahadur Adhikari, a Nepalese who grew up in the Himalayas; Valerie La Breche and my husband, Bill, both raised in Alaska; and myself. We were old friends who had traveled together before.

A few years earlier, on a canoe trip down the Yukon River from Whitehorse to Dawson, Yukon Territory, we had worked out a river routine that served us well. We learned that pacing is the secret of success. A hearty breakfast followed by a mid-morning break for a stretch and a snack, a half-hour nap after lunch, a cup of tea before setting up camp, a drink, dinner, then fishing or reading or berry-picking, and a perfect day is completed. Not all of the days worked out quite so smoothly, of course. A burst of rain, rapids to run or, worst of all, not being able to find a suitable campsite could throw our leisurely routine off a bit.

Now we were back in the Far North country, and we had gotten off schedule the night before and unwittingly camped smack in the middle of the migrating caribous' route south. Right in the grizzly's hunting grounds.

We had planned to camp the fourth night out at New Ramparts, a deserted Hudson's Bay Trading Post on the Canadian-Alaskan border. There were no rapids on the river to hold us up, but our first day was shorter than we had planned. Getting to Old Crow, where we put into the Porcupine River, had been our biggest problem.

We had met in Fairbanks, Alaska, and driven 135 miles north to Circle Hot Springs, where there is a delightful resort consisting of a recently restored log roadhouse with 40 rooms done up in Gay Nineties decor, several log cabins, a general store and a huge outdoor swimming pool fed by the hot springs. There we gorged on salmon and steak dinners with all the trimmings, marveled at the huge yellow tuberous begonias, orange nasturtiums and purple petunias cascading from the window boxes and gawked at the grizzled miners and trappers in the bar. In the evenings we floated on our backs in the relaxing warmth of the pool and gazed up at the huge slate-blue dome of the arctic sky. Here, the summer sun never sets and the soft pinks, corals and lavenders of twilight linger all night.

We allowed ourselves two days and three nights at Circle Hot Springs to unwind and organize our gear. By the second evening we had sorted and repacked everything we needed for 16 days on the river: the dried food, tents and sleeping bags from the three footlockers we had shipped ahead, clothes and equipment we brought with us, plus the food we bought locally. It was all stuffed into two four-foot canvas duffel bags, one three-foot waterproof duffel and 13 cardboard cartons; and we each had one small day pack. Total weight: 334 pounds.

Regretfully we left out the bacon. We had started every morning along the Yukon River with the delicious aroma of bacon cooking over our campfire. But the Porcupine River was in wilder country, more remote, without a single inhabitant along the length we would travel. And old-timers at the hot springs had regaled us with stories of how the smell of bacon brought bears bounding over mountains straight into camp. We scratched the bacon.

We had learned on the Yukon trip that Jane had her own deterrent to snooping bears. Every night she circled each of our tents with a ring of small white mothballs. Then, being of thrifty New England ancestry, she salvaged them each morning from the sand or moss.

Now we were in the bar joshing Jane about bringing along the same old mothballs for this river trip, and we had our first setback. A message came that the pilot we had contracted to fly us to Old Crow had had a fight with his girl friend and left the country -- with his plane!

No real Alaska bush pilot would leave us in the lurch, all the old-timers assured us. This fellow obviously was a newcomer. But he was gone and we had a schedule to keep.

Alaska has very reliable bush airlines, but none runs a scheduled flight out of Circle Hot Springs. We had to arrange two charter flights, one for us and one for our freight, with a pickup stop at Fort Yukon for the two canoes and two kayaks we had rented there. (We would have preferred to have three canoes for the six of us but that would have entailed a third plane trip, since the canoes were to be carried lashed onto the plane's pontoons -- one canoe for each pontoon.)

Glumly we walked up the hill behind the roadhouse to reconsider our situation. At the top of the hill was a little cemetery enclosed by a picket fence. Some of the several dozen simple wooden markers poking up at angles from the weeds and wildflowers carried no names. Typical inscriptions were, "Died winter of 1938-39. About 80" or "Bones found 1931 -- Porcupine Creek." We felt very far north.

Bill spent the next day on the telephone trying to roust up a plane. We had all piled into bed when, about 11 p.m., he came down the hall, knocking on our doors and calling out, "All's well! Flight out 8 a.m. tomorrow."

The pilot flying the Cessna 206 float plane needed as light a load as possible to carry the canoes. The other plane -- a seven-seat Cessna 207 that would carry us -- was limited to 1,200 pounds. Carrying our packs we weighed in on the roadhouse scales and found we could add to the 207 five boxes of groceries, our tool kit, a bag of ammunition and fishing rods to reach the limit. That left only 200 pounds of freight for the Cessna 206.

Squeezing into our little plane, almost buried beneath our gear, we took off in a spray of gravel from the Circle Hot Springs landing strip.

Flying at about 7,000 feet, we headed northwest to Canada over row after row of mountains sweeping up like waves with sharp crests. After we crossed the Arctic Circle, the lanky young pilot began scanning the map on his lap with unsettling frequency. Below, as far as the eye could see, there was not one sign of human habitation. In about an hour we were out of the dark green spruce-covered mountains and over flat country dotted with thousands of lakes and ponds. The only trees edged great looping rivers.

Another 45 minutes and we spotted the tiny settlement of Old Crow, an Athapascan Indian village 250 miles north of the Arctic Circle, strategically located on the migration route of 120,000 to 140,000 caribou that comprise the great Porcupine Caribou Herd. In early spring the caribou drop their calves on the icy shores of the Arctic Ocean, then in summer slowly drift south across the tundra of Old Crow Flats and the Porcupine River to winter in the mountains.

The Royal Mounted Police officer at Old Crow checked our identification and gear, explaining that he had to check for incubators. He told us about smugglers who carry peregrine and deer falcon chicks across the border for sale to falconing enthusiasts for $50,000 to $60,000 a bird. Perhaps none of us seemed to him young and agile enough to scale the cliffs and rob nests in this risky business.

For two hours Valerie, Bill, Carl and Bir struggled to assemble the folding Klepper kayaks, as Jane read aloud the turgid directions that we decided were a direct translation from the German.

I went in search of Stephen Frost, an Athapascan representative on the International Porcupine Caribou Commission, a volunteer group of Inuits and Athapascans from Alaska and Canada that first met in Old Crow in 1978 to find ways to protect the caribou herd. Now, with the support of the Friends of the Earth and several Inuit and Indian groups, they are working for an international protection treaty.

Frost was a lean, strong man my age with a brown, weathered face that remained utterly impassive while I explained who we were and how we were going down the river and did he think we might see some caribou? Then I mentioned my uncle, Jim Dodson, who had been an Alaska bush pilot, pioneering air routes to the Porcupine River area in the 1930s when fur trapping was a good business. (It no longer is.) Slowly a smile lit Frost's face. "Jim gave me my first plane ride. He was a good man," he said. Then he shook my hand.

When I joined the group on the river bank, they had finally produced two very small-looking kayaks from the assortment of poles, boards and canvas. Since none of us had ever been in a kayak and were not eager to try them, we drew straws. Bill and I got the short ones.

By now it was late afternoon. We pushed off into a headwind and quickly learned that kayaks are very sensitive to any load shift.

The Porcupine River was the highest it had been in years. It was running about three miles an hour and since we estimated we could paddle about the same, we counted on making six miles an hour. With 360 miles to go, we planned on doing about 25 miles a day for 14 days with two rest days -- a comfortable four to five hours of paddling each day.

But that first short day we managed only a little over an hour. Brush and uprooted trees floating down the river and sweeps hanging from the banks around every bend made maneuvering tricky. Seagulls hovered over us as if we would momentarily turn into scraps they could salvage. That night we slept nine hours.

The wind kept up. Valerie and I tied our hats down with bandanas. The river was a corkscrew twisting through the tundra, its banks giving way to mud slides streaked with ice. We were layered in long underwear, jeans, T-shirts and windbreakers, but by afternoon the wind ceased and under the warmth of the close arctic sun we peeled off jackets and shirts.

The second night we camped on the narrow ledge of a 10-foot bank and nearly lost Valerie. A storm blew up with winds so strong that her tent pegs wouldn't hold and her 105 pounds weren't heavy enough to keep the tent from lifting and rolling. She was headed for Oz the way Dorothy left Kansas when Carl braved the storm to secure her.

Finding campsites always is the biggest problem on a river. The night before the grizzly appeared we had left the tundra and were in canyons with 75- to 150-foot-high cliffs. There were few banks level enough to make camp. It was late before we found a long sandy strip with willows behind it and a small waterfall. Bir cut some of the willow brush with his kukri, a short curved Nepalese sword, for our beds and we fell into exhausted sleep.

The next morning Valerie awakened us whispering, "Shh! Caribou!" I poked my head out of the tent and there stood four beautiful stags with flaring antlers about 75 feet away, their big brown eyes staring in surprise at us. We stared back for what seemed like a very long time. Then they trotted along the river's edge, leaped into the water, swam across -- holding their little white tails straight up like pennants -- climbed out on the opposite shore and gracefully ran almost straight up the 45-degree cliffs.

All morning the caribou ambled out from the woods behind us in groups of twos or tens or twenties. They were not afraid. We watched, enchanted, warmed by the sun and lulled by the peaceful beauty of this wilderness scene.

The sudden roar of the grizzly was a shock!

The bear swam to our side of the river. It got out of the water about 150 yards downstream, shook its massive body and started running toward the woods. Suddenly it veered and with a spine-chilling roar charged us.

We were lined up with the fire behind us, shouting and banging our pots, to no avail. Carl had the only gun. But he hadn't been hunting for a decade and had never hunted bears. Bill yelled, "Carl, SHOOT!"

But Carl coolly waited until the grizzly was about 100 feet from us. Then he shot once over its head. The bear turned, its powerful flanks heaving, and headed back to the river.

Fifteen minutes later three more grizzlies, probably the rest of the family, showed up. Fortunately they all stayed on the other side of the river, loping up and down the bank and rearing up to roar their displeasure at our being there. We agreed it was the wrong place to be and broke camp as fast as we could.

The rest of the trip was serene. The sun shone and not even the notorious Alaskan mosquitos bothered us.

On our rest day at New Ramparts, Stephen Frost, his wife, niece and two sons appeared. The caribou, silhouetted against the sky at the top of the cliffs behind us, continued to stream down and swim the river. In one hour I counted 258.

Frost's son shot a buck without disturbing the others. With the skill of surgeons, the men quickly skinned and cleaned it. They presented us with the liver, which Valerie marinated in oil and herbs, and we ate it for several days.

We fished, picked wild raspberries, blueberries and low-bush cranberries, took our naps in mossy groves of juniper and spruce and drew deep breaths of crystal-clear air sweetened with the spicy citrus-like fragrance of the ubiquitous chamomile plant growing on gravel bars. We explored deserted trappers' cabins.

For more than 300 miles we met no one. In the glorious silence all we heard was the river running, loons crying and geese honking overhead. "There's almost too much beauty to absorb," Jane said.

Every day we felt stronger and more at peace with the world. Exactly at noon on the 16th day, just as planned, we paddled into Fort Yukon. Old-timers now. Tough and durable.