In one of the most spectacular accidents of the Space Age, a five-ton Soviet surveillance satellite with an atomic power plant aboard burned up in the atmosphere yesterday over the remote reaches of Canada's Northwest Territory.

Presumably, the 110 pounds of uranium that fueled the power plant and the radioactive strontium, cesium and iodine that were the fission products of the uranium burned up with the satellite so high in the atmosphere that they were scattered to the four corners of the Earth.

"Chances were 98 per cent that it dissipated as it fell through the atmosphere," Canadian Defense Minister Barney Dawson told a news conference in Ottawa. "We have been advised that the danger of radiation [WORD ILLEGIBLE] minimal."

The Soviet craft began its plunge into the atmosphere at 6:50 a.m. EST over Queen Charlotte Island off the west coast of Canada and disintegrated three minutes later into countless fireballs over Great Slave Lake, near the mining towns of Yellowknife, Fort Radium and Uranium City.

"I saw a white ball of fire," said Dale McLeod, a Royal Canadian Mounted Policeman on patrol along the southern shore of Great Slave Lake. "I saw a red light and then some small balls of fire that I was able to watch for some distance."

"There was a main part, like a bright light, and lots of small parts trailing behind it," said Mario Ruman, who runs a janitorial service in Yellowknife. "The main part was like a bright flourescent light, and each part had a long, bright tail. None of them made a sound."

By 11 a.m. yesterday, search parties were out along the shore of Great Slave Lake looking for any debris that might have fallen to Earth. In northern California, the U.S. Air Force dispatched an instrumented KC-135 jet from McClellan AFB and a high-flying U-2 aircraft from Beale AFB to sample the air over western Canada for radioactive fallout.

The planes were due back at their home fields around midnight last night, at which time the filters they carried to trap radioactive debris from the upper atmosphere were to be removed and analyzed for radioactive isotopes like strontium-90, consium-137 and iodine-131 that are the fission products of any nuclear chain reaction.

"The radioactivity we might find is like you'd see from the blast of a very small nuclear bomb," said Ben Huberman, a staff member of the National Security Council. "It would be as if they exploded a bomb at a very high altitude and then the debris just floats around the Earth for years."

The Soviet satellite was described by White House and congressional sources as an "ocean surveillance satellite" that uses radar to locate warships of the U.S. Navy in the major oceans. The five-ton satellite that broke up yesterday was the first of 16 ocean-surveillance satellites to meet with an accident in the last six years.

Launched from the Soviet cosmodrome near Tyura Tam last Sept. 18, the satellite was called Cosmes 954 by the Soviet Union. It followed into orbit a sister satellite named Cosmos 952, which left the cosmodrome two days before on Sept. 16.

Both satellites had been flying 150 miles above the Earth in a northeasterly direction, following a path that took them over roughly two-thirds of the Earth every two weeks. The limits of their surveillance were the edge of the Antarctic in the southern hemisphere and the edge of the Arctic in the northern hemisphere.

Around Christmas, Cosmos 952 was fired out of its 150-mile-high orbit and raised to where it circled the Earth at an altitude or more than 600 miles. The same maneuver had been performed by 14 earlier ocean-surveillance satellites to take them and their atomic reactors far enough from Earth to keep them in space for 600 years.

In the six years the Soviets have had their ocean-watching satellites in space, they have always had two on patrol at the same time. The longest any has stayed in the 150-mile orbit hascbeen 74 days. Most stay in orbit no more than two months before being lifted to the higher orbit where they are no longer operational.

A few days after Christmas, the same orbit raising manouver was tried on Cosmos 954. The satellite failed to fly into the higher orbit. One source said the engines of Cosmos 954 may have kept firing instead of turning themselves off, forcing the five-ton craft into a tumble that brought the satellite out of orbit.

Reporting from Moscow, Washington Post correspondent Kevin Klose said the Soviet News Agency Tass said the satellite "was sharply depressurized for reasons yet unknown on Jan. 6 this year, with the result that the satellite began to come down in an unplanned regime."

This would suggest that the satellite's fuel tanks had been exhausted, either by a leak or some kind of explosion that did not allow the satellite's engines to fire. The leak or explosion could have been enough to give the satellite a "downward" thrust that would begin to take it out of orbit.

About this time, the North American Air Defense Command at Colorado Springs began to notice that Cosmos 954 was in trouble. Radars operated by NORAD saw the Soviet satellite fall from 150 miles to 100 miles in 10 days, at which time warning were flashed to countries like Canada and Denmark, which lay below the satellite's track.

Intelligence sources have known for some time that the Soviet ocean-surveillance satellites get their power from nuclear reactors. Sources said the reactors hold 110 pounds of highly enriched uranium, the same kind of fuel used in atomic submarines and the same type of uranium used to make nuclear bombs.

That much uranium produces at least 100 kilowatts of electricity, enough to power an active radar system that could penetrate clouds to identify surface ships bigger than a tugboat anywhere in the world. It could distinguish targets as different as an aircraft carrier or a surfacing nuclear submarine.

The satellite's nuclear power plant was presumably "turned on" shortly after the satellite left Earth last September and kept on at least until Christmastime, when it was due to be taken into a higher orbit. If so, the satellite's reactor would have produced about 100,000 curies of fission products like strontium-90 and cesium-137. These are the poisonous wastes of nuclear power.

At best, these wastes were burned up with the satellite over western Canada at such high altitudes that they were taken by upper air winds and carried all over the globe where they might stay for years to come. At worst, they settled down toward Earth with rain and snow that brought them to rest on pastureland across the northern reaches of western Canada.

The fission product called iodine-131 is the first one nuclear sleuths look for in the fallout of an atmospheric bomb test and it is the first one they will look for in yesterday's satellite mishap. The iodine settles in pasture grass, then seeks out the thyroid glands of cattles eating the grass. The milk of cows grazing on contaminated grass has often been destroyed after an atmospheric bomb test.

The flight of Cosmos 954 was not the first misguided satellite with atomic fuel aboard. The United States has had three accidents involving nuclear-fueled satellites, only one of which involved the burnup of radioactive debris.

That took place in 1964 when a Navy Transit satellite burned up in the atmosphere, spewing into the upper air reaches 17,000 curies of radioactive plutonium that had been used as a heat source by the satellite.

Twice since then, radioactive heat sources have plunged back into the water along with pieces of the satellites that took them away from Earth. Both were recovered intact by Navy frogmen.

One was the radioactive source aboard the Apollo 13 spacecraft that never made it to the moon. The other was aboard a Nimbus weather satellite that failed to go into orbit and fell into the Santa Barbara Channel off the coast of California.