Radar tracking indicates an abandoned Soviet space station will plunge back to Earth late Wednesday or early Thursday, but officials said any chunks of the 21-ton craft that survive the hellish re-entry likely will fall harmlessly into the ocean.

The Salyut 7 space station, launched April 19, 1982, was abandoned June 25, 1986, after major efforts to fix a variety of problems plaguing the aging orbital outpost, which was designed to have a lifetime of just four to five years.Tom Niemann, a spokesman for U.S. Space Command in Colorado Springs, said radar tracking indicates the cylindrical space station and an abandoned re-entry module likely will fall into the atmosphere sometime between 2:18 p.m. MST Wednesday and 2:18 a.m. Thursday.

The actual computer projection, subject to change, listed re-entry at 8:18 p.m. Wednesday, plus or minus six hours. Should re-entry actually occur at 8:18 p.m., pieces of the space station would fall harmlessly into the Pacific Ocean well east of New Zealand, Niemann said.

"There is a re-entry module on board that weighs about 3 tons," he said. "So it will likely survive re-entry. Right now, the most likely area is over the Pacific Ocean, which certainly minimizes the risk to populated areas."

Despite the small risk, the Federal Emergency Management Agency in Washington said it was monitoring the re-entry so the agency could warn state and local governments if debris were to land in the United States.

"Although there are few protective actions which could be taken should a large piece of the space station strike the ground . . . state and local planners need to be kept informed and advised until the satellite no longer poses a threat," the agency said.

As of Tuesday, radar tracking showed Salyut 7 in an 88-minute orbit tilted 52 degrees to the equator with a high point of 111.2 miles and a low point of 107.5 miles. For comparison, space shuttles typically operate at altitudes of 160 miles or so.

It is believed that Salyut 7 was built as a backup to Salyut 6 and later modified for space flight. It ultimately was launched by a Proton booster from the Baikonur Cosmodrome in Soviet Central Asia.