A decade ago they said it would destroy America's last virgin wilderness.

The trans-Alaska pipeline would slash an 800-mile wound from the caribou habitats of the Arctic to the salmon-rich waters of Prince William Sound. Its construction crews would destroy irreplaceable fishing streams, its hot petroleum would melt the fragile permafrost, and its leaky tankers would turn the waters around the southern Alaskan port of Valdez into one huge oil slick.

U.S. conservation groups united in one of the great environmental battles of the 1970s to try to stop the pipeline in Congress and in the courts. They lost, and the most expensive privately financed construction project in history was completed five years ago. The pipeline has since pumped 2.4 billion barrels of oil out of the Arctic, filled 3,000 tankers at Valdez and now brings America 17 percent of its oil. But none of the major environmental disasters predicted for the pipeline has come to pass.

The pipeline has revolutionized much of life in Alaska, flooding the state treasury with money, adding thousands of jobs and giving people unprecedented access to their northern wilderness. But the caribou and the salmon have continued to follow their annual journeys across the snow and through the seas. Alders have grown back to hide the gleaming steel pipe in many places and scientists hold their breath in hopes that it will all remain this way.

In fact, because of the widespread concern about the pipeline's potential problems and because of some of the most advanced engineering work of the day, the Trans-Alaska Pipeline System has been turned into a technological wonder of environmental protection, boasting a series of sophisticated leak detection and spill prevention devices unexcelled in the world.

In 1981, the Alyeska Pipeline Service Co. loaded 735 tankers with 22,975,094,016 gallons of oil. But only eight gallons of oil -- less than even one barrel -- spilled into the water, according to Alyeska marine superintendent and former Coast Guard commander James K. Woodle.

Although John F. Ratterman, public affairs manager for Alyeska, said that company engineers were determined to protect the environment from the beginning, he credited environmentalists with "promoting an acceptance of the need for the protection of wildlife for its sake alone -- quite aside from any engineering considerations."

This led to raising the pipeline 10 feet in the air at some points for big game crossings and led to the company taking great care that construction would not disturb the habitat of mountain sheep.

"I would say overall in regard to oil spills, it could have been worse," said Lyn Sonnenberg of the Sierra Club in Juneau.

Roland Shanks, chairman of the Alaska Sierra Club, said, "A lot of the questions that were asked became problems that were solved before the pipeline was built."

"I think the focus of environmental groups has shifted to other issues," said Jana Baumann, a public relations officer with Alaska's environmental conservation department.

Initially, the pipeline was to be buried underground for more than 90 percent of its length. Environmentalists argued that heat generated by the 90- to 145-degree oil would melt and permanently ruin the permafrost, the fragile layer of frozen earth covering much of northern Alaska, and cause widespread damage to wildlife and vegetation.

Today, only about half of the line is buried (some of that refrigerated to protect the permafrost), incidentally making leaks easier to identify and repair.

If anything associated with the pipeline is likely to seriously harm the environment, conservationists and government officials here say, it is not the gleaming steel 48-inch pipe but the haul road -- called the Dalton highway -- which was built to construct and service it.

The state has made a controversial decision to allow public use of the road, which begins near here, to a point 211 miles north at Disaster Creek, about halfway to the Arctic Ocean.

The pipeline has had some environmental impact, said Larry Dietrick, pipeline monitor for the state's environmental conservation department, but "if you had the pipeline going up without the road, I would say the impacts were mitigatable and acceptable."

The haul road allows about 200 trucks a day to carry supplies to the oil fields on the Alaskan North Slope near Prudhoe Bay. But during summer months when it is open to the public, some independent miners searching for gold have been able to truck their bulldozers to hitherto unreachable streambeds and scoop out soil and gravel.

Bears used to flock to the pipeline where hunting was prohibited and pipeline workers often left food behind. Now hunting with permits has returned and few bears are seen in the area. Only archers may hunt big game within five miles of the haul road, but firearms are allowed beyond that.

State officials in charge of conserving wildlife also worry about the future spread of the oil fields at Prudhoe Bay, which they say have already forced the central Arctic caribou herd to give up some favorite calving spots. According to Ray Cameron, a game biologist with the U.S. Fish and Wildlife Service here, the caribou have long preferred the bleak Prudhoe Bay area because they were relatively safe there from predators and harmful insects like mosquitoes, warble flies and other flies called nose bots.

Before the oil men began to pump crude out of Prudhoe Bay, some naturalists predicted the project would force the caribou to abandon the area. "As far as we can tell," said Cameron, who has been studying the caribou in the area since the pipeline project began, "that sort of thing has not come to pass."

Oil spills on land have been more serious than those at sea, but still far less than pipeline critics predicted. Shifting, melting ground near the Atigun Pass opened a crack in an underground section of the pipeline in June, 1979, and an estimated 1,500 gallons spilled out before the leak was discovered. The worst -- and most mysterious -- break occurred on Feb. 15, 1978, when someone, in an apparent act of sabotage, blew a hole in the pipeline near here that spilled about 550,000 gallons of oil.

No one ever claimed responsibility for the explosion. It forced a massive cleanup, including a burnoff of much of the oil that had spilled. But Arlan H. Kohl, the U.S. Bureau of Land Management's pipeline project manager in Anchorage, said he was amazed when he visited the site recently. At first he thought the staffer who had taken him there was lost "because I couldn't see any evidence of [the spill] . . . . The alders covered completely the lower half of the pipe . . . . The grass was back, the birds were chirping. I was really, honestly flabbergasted," he said.

The pipeline cost $8 billion in all, $3 billion of which Ratterman attributes to inflation caused by the delay in construction because of the fights against the project.

Kohl said the Alyeska company has steadily improved its ability to detect leaks through a series of computer-controlled monitors that measure the volume and pressure of oil flowing through the pipe. The special-quality steel used has allowed the pipe to jump off its supports during one early pressure surge and still not crack open.

But officials here do not discount the possibility of a sudden, catastrophic accident. The pipeline's success so far, said state environmental field officer Jeff Mach, "you could attribute to good engineering or you could attribute to luck."

In January, 1980, a drifting, fully loaded tanker came within 1.4 miles of hitting a shoal and breaking up before its frantic crew managed to restore power to its engines in Prince William Sound.

Kohl said that the pipeline also is certified by experts as earthquake-proof up to an 8.5 magnitude tremor on the sliding Richter scale, but "personally, I don't know how anybody on earth can say whether it is or isn't. We'll just have to wait until an 8.5 quake to see."