A mysterious Soviet satellite that changed orbits at least five times fell to Earth and burned up in the atmosphere last week after 200 days in orbit, according to western scientific sources.

The satellite was named Cosmos 929 by the Soviet Union, which flew it in an orbit very close to the path followed by the Soviet manned Soyuz and Salyut spacecraft.The Soviets never identified Cosmos 929's mission which U.S. space experts believe was to serve as a "space tugboat" to bring together big pieces of space machinery.

Launched seven months ago by a Proton rocket, Cosmos 929 fell in a fiery re-entry over the Pacific Ocean last Thursday, the sources said. Pieces of the 20-ton satellite that did not burn up in the atmosphere would have fallen into remote regions of the Pacific.

The Soviets reportedly maneuvered Cosmos 929 at least five times by remote control, each maneuver raising or lowering the satellite's orbit by no less than 60 miles and no more than 100 miles. The major maneuvers took place last August and September, when it climbed to an altitude of almost 300 miles above the earth.

In January, the satellite was lowered into an orbit about 130 miles above the earth and on Feb. 2 it was commanded to burn its onboard rocket engine in a way that brought it back into the earth's atmosphere over the Pacific.

U.S. experts believe Cosmos 929 was the first test of what the Soviets call "space crane," designed to move large objects around to assemble a spae station in orbit. Another piece in the space station plans of the Soviet Union, the cargo ship Progress 1 that had been docked with Salyut 6 in orbit, fell into the atmosphere over the Pacific yesterday.