Soviet sources said here yesterday that Soviet fighter pilots were specifically ordered by Moscow to fire missiles at a Korean Air Lines plane and bring it to earth last Thursday as it strayed unknowingly over Murmansk, a strategic military port.

These sources said the Soviet air defense command feared the plane could be an intelligence aircraft posing as an airliner, seeking information about the many military installations in the Murmansk area, bulwark of Soviet northern defenses in the Kola Peninsula.

About 400 Soviet submarines, including nuclear-powered vessels with Intercontinental nuclear missiles, are based at the closely guarded port.

The sources said the decision was made in Moscow to force the plane down by firing on it, but to bring it down in a condition that would permit a thorough examination of it.

They suggested the Soviets became convinced - as the plane continued south at 35,000 feet, unresponsive to repeated radio queries from ground stations and circling interceptors - that it would suddenly turn west and flee to safety over the nearby Finnish border, carryiing with it valuable intelligence data picked up by electronic gear presumed to be in the plane.

The unarmed Korean Boeing 707, carrying 110 passengers and crew, was ripped by an explosion that killed tow and injured 10 and forced it to land on a frozen lake near Kem, south of Murmansk.

The Soviet sources said the plane was hit by a missile that was shot at it. The missile apparently exploded on or near the rear edge of the 707's left wing, spraying shrapnel into the cabin.

There is no way to check the veracity of this Soviet account, but it is remarkably similar to one given independently Monday by a Norwegian NATO officer who was reported in several London newspapers as saying that a missile fired on direct command from Moscow apparently exploded in the vicinity of the airliner.

THe sources for the Soviet version of the incident are Soviets who have made a practice of speaking to Western journalists informally and are considered here - where access to officialdom is scant - to be able to speak out authoritatively on certain matters from time to time.

The Soviet sources said two fighter planes were sent to intercept the liner near the Soviet mainland as it headed south across the Barents Sea, drastically off course.

The sources said the fighters circled and singalled with landing lights, then fired across the nose of the plane with tracer bullets to warn it to land. When there was no response, the air-to-air missile, possibly a radar-guided ANAB, was fired. The Soviet account that surfaced here yesterday does not provide a time sequence for the fatal events that unfolded after the interceptors met the plane.

Passengers interviewed at Helsinki told of seeing a single interceptor flying on the right side of the plane, then of sparkling lights moving past them on the left side, and then the exmore than 20 minutes.

The South Korean co-pilot, S. D. Cha, said he saw a Soviet fighter flying close to the nose of his plane and that while it had made a signal, he did not understand its meaning beyond fearing that it was threatening.

According to the Soviet version, the plane was fist spotted by ground radar stations in the vicinity of Franz Josef Land, a group of Soviet islands lying above the 80th paraelle, 700 miles north of Murmansk.

The stations began querying the plane on every available commercial radio frequency, but it did not respond, the sources said, and as Korean Air Lines Flight 902 continued inexorably south, the decision was made to scramble fighters. One of these has been identified as a Sukhoi-15, a missile-firing interceptor from a photograph taken from plane window by a Japanese passenger.

The Soviet sources said that the airport lights in Murmansk has been turned on the chance that, if the plane really were a civilian jetliner, it would land there. Passengers and crew, however, had made no mention of seeing any airport lights.

The area north of Murmansk has long been sensitive to the Soviets as well as to NATO. Military reconnasterance aircramt and ships from both countries continually ply the air and waters, seeking to test the readiness of each other's defenses and to determine the size and number of military units. An American RB-47 reconaissance bomber was shot down here by Soviets with the lost of six crewmen in the early 1960s.

According to other news accounts, the tracking stationt at Bodo, Norway, saw a southbound plane enter Soviet airspace well to the north of the mainland, but assumed it was Soviet. The Korean plane, on a flight from Paris to Seoul with a refueling stop at Anchorage, Alaska, should have been continuing north over the pole.

But through a so-far unexplained gross navigational error, the plane had swung around and traveled back south, but dangerously east of its original flight path.

The Korean pilot, Capt. Kim Chang Kyu, was so disoriented that the had reported to an air traffic contrl station at Spitzbergen in Sralbard, 400 miles of Norway's North Cape, that he was over Greenland.

He asked controllers to report his position to a ground station at Keflavik, Iceland, saying he could not get through due to atmospheric conditions. The Spitzbergen station did not question his error of position.

By that time, he was so far off course that the Bodo tracking station throught his was a Soviet plane.

The radio trouble reported by Kim may help explain why he apparently did not hear and did not - or could not - respond to the urgent queries the Soviets say they made.

The account by Soviet sources yesterday partially dovetails with an official Tass statement issued Friday that asserted that the plane was over Soviet restricted air space for two hours before landing. The Tass statement said the Soviet fighters signaled the plane to land but it did not mention that the interceptore had fired on it or that two passengers had died in the attack.

The Kremlin has made no further official mention of the incident.

Pilot Kim and navigator Lee Kun Shik, both veterans of transpolar flights, have been detained by the Soviets and are now in Leningrad being questioned. The other members of the crew and surviving passengers were released and have left the Soviet Union.

The Soviet sources offered as an exculpatory explanation the assertion that had the commanders wanted to destroy the plane, they could have fired on it from the ground or ordered the Soveit fighters to make another firing run.

But uppermost in their minds, these sources suggested, was the notion that the plane was an intelligence craft and they wanted to know what it had found out. So they ordered it damaged and forced down, not destroyed in the air.

They suggested that one ingredient in this thinking among commanders of a nation notable for its suspicion and fear of losing military secrets was that Western intelligence agencies had seized upon the visit here last week of Secretary of State Cyrus Vance as an opportunity to penetrate Soviet defense perimeters.

By this reasoning, the foreign agencies would be confident that the Soviets would not shoot at such a plane for fear of creating an embarrassing incident while Vance was here.

Recording devices in the plane that could tell much about the Korean crew's conversations and the plane's maneuvers were removed by Soviet troops.

Korean Air Lines, meanwhile, said yesterday that in the furture for its polar flights it would use only DC-10s, which have sphisticated computerized navigational systems, rather than the older 707s.