Two Soviet cosmonauts landed safely on earth yesterday after a 96-day space flight, a new endurance record with major implications for Moscow's manned exploration of space.

Yuri Romanenko and Georgi Grechko made an uneventful soft landing on a snowy field in Kayzakhstan just three hours and 19 minutes after undocking their capsule from the 19-ton Salyut 6 space station. It had been their home since Dec. 11, the day after they rocketed into space central Asia.

The two men were reported by the official news agency Tass to have "stood up well to the prolonged orbital flight," according to a preliminary medical checkup. The previous space Americans of skylab 4, who spent 84 days away from the earth. They reported no lasting ill effects of their sojourn.

Grechko, 46, the flight engineer and a national television personality after almost nightly telecasts from orbit, now holds the individual record for most time in space - 126 days. This is comprised of 96 days aboard Salyut 6 and 30 from an earlier flight aboard a Soyuz spacecraft.

"A wide range of important science tific and technical studies and experiments have been carried out during the long manned flight of Salyut,"said Tass. "A considerable part of the flight was devoted to the study of natural resources and the environment. The cosmonauts repeatedly photographed the territory of the Soviet Union."

Other studies included the growing of crystals under space conditions of vacuum and weightlessness and attempting to devise new alloys of metals. This was "an important part of the program," Tass said.

Western scientific observers are most interested in the results of these experiments, as they may have demonstrated that new and useful materials can be manufactured in space. the space station's systems, the Tass said, to await further use later this year by new teams of cosmonauts. The Soviet used this Salyut flight to test successfully several new space techniques.

In all, they sent four different space vehicles to the station, docked them and showed that they have achieved their goal of multiple simultaneous spaceflights. After Romanenko and Greckho were aboard, they were visited by two cosmonauts on Jan 11, an unmanned cargo ship on Jan. 22 and two other cosmonauts on March 3.

On Feb. 2, the two men transfered volatile and dangerous rocket fuel and oxidizers from the cargo craft, a space first. The March 3 visit carried a Czechoslovakian crew member, the first non-Russian, non-American to go into space.

During the flight, Romanenko and Grechko did special exercise to keep their bodies fit in a weightless state. Grechko apparently underwent a slight heart irregularity, but U.S. space scientists familiar with the Skylab flight of 1973-74 reported similiar abberations witout ill effect.

The two cosmonauts are sure to be showered with medals and honors, including busts of themselves in their home towns.

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