The Great Space Mystery deepened yesterday as Canadian and American scientists fell back on their original assessment that little or no radioactive fallout had reached the ground from the Soviet satellite that burned up in the atmosphere Tuesday over Canada's Northwest Territories.

The "extremely dangerous" radiation that had been pinpointed on the ground near Baker Lake on Thursday was blamed yesterday on faulty airborne instruments that had been flown over the Baker Lake region.

New instruments flown over the same region yesterday could not confirm any radio-activity except low-level radiation from a natural outcrop of radium along the shores of the lake.

At the same time, at least two and as many as four unexplained radioactive "hot spots" were sighted along the shores of Great Slave Lake west of Baker Lake and quite close to the predicted path the fallen Soviet satellite would have taken as it broke up.

By last night, giant twin-engined Chinook helicopters were flying airborne gammaray detectors on low-level passes over the four sites to get better readings of what C-130 Hercules aircraft had picked up from higher altitudes. The trouble with the four hots spots was they were all located along a landscape where uranium has been found and mined.

"It is unlikely," Canadian Chief of Defense Admiral Robert H. Falls said in Ottawa late yesterday, "that there is anything on the ground."

Unlikely as it might be, the possibility that there is "something" on the ground was not being dismissed yesterday for all the defense officials and scientists engaged in a hunt that was taking them and their instruments over frozen tundra 1,000 miles long and 100 miles wide.

One of the search leaders, Canadian Col. David Garland, said nobody knows how much of the fallen Soviet surveillance satellite and how much fits uranium nuclear power plant burned up in the atmosphers.

"It could be that the whole package is on the ground," Garland told a news conference in Edmonton. Alberta which is serving as command post for the Canadian and American Canadian and American "nuclear response" teams. "Or it could be one hundreth o fit is on the ground."

Before Canadian officials blamed Thursday's report of "extremely dangerous" radiation on faulty instruments, American scientists helping in the search for radioactive debris suggested that the Baker Lake hot spot disappeared because the fallen debris melted through the tundra.

David Jackson, spokesman for the Department of Energy team from the Nevada Test Site, where the U.S. tests nuclear weapons underground, said it was possible that radioactive debris was so hot that it burned its way beneath the permafrost in the tundra around Baker Lake. If so, ice and water could be insulating the radiation from the airborne detectors that picked it up the first time around.

Later, Falls blamed the whole Baker Lake sighting on faulty gamma-ray detectors that had been flown over the region on Thursday.

"This equipment is very delicate and it is a very hostile environment," Falls said, referring to temperatures around Baker Lake that had plummeted to almost 50 degrees below zero.

Jackson said the radiation was first seen by a C-130 airplane from an altitude of 1,500 feet Wednesday night. He said the plane made three "hits" of gamma-ray radiation on the three passes it made over uninhabited tundra 200 miles west of the settlement of Baker Lake.

Baker Lake is inhabited by 1,000 people, some of them Royal Canadian Mounted Policemen. Most of them are Eskimos who make their living trapping and fishing. The region is so bleak west of Baker Lake that even the caribou leave in the winter. The tundra was described yesterday as looking "like a white sheet on a billiard table."

While 12 passes had been made last night by C-130 planes around Baker Lake and Great Slave Lake, high-flying U-2 airplanes equipped with filters searched the upper atmostphere for radioactive fallout. They had found nothing in the upper air reaches that even resembled fallout.

White sources began insisting last night that it was likely that the 10,000-pound Cosmos 954 satellite had been completely burned up when it descended into the earth's atmostphere on Tuesday. One source said this was what the Soviets told the White House when they were asked and that there was no reason to doubt the Soviet reply.

Whatever radioactive debris reached the ground, the White House source said, could have been the estimated 100 pounds of graphite that served as the "moderator" for the 110 pounds of uranium that fueled the satellite's nuclear power plant. Graphite is extremely resistant to heat, even the 2,000 degrees Fahrenheit that would build up on the satellite from friction with the atmosphere on re-entry.

"The graphite might be highly radioactive for a short period of time," the source said. "This might be what the airborne in struments are picking up."

In a letter to President Carter, nuclear critic Ralph Nader asked yesterday why public health officials were never notified of the falling Soviet satellite which Nader said could have "landed or vaporized over a major urban area" along the path it had flown.

"Inasmuch as the U.S. government discovered the existence of this problem as early as Jan. 12," Nader said, "it is rather unsettling to discover that statewide public health officials were never notified that a radio-logical accident was imminent. . ."

The president made no reply to Nader's letter but he did criticize the Soviet Union for not warning the world sooner that Cosmos 954 and its atomic power plant were about to fall from the sky.