Three Soviet cosmonauts returned safely today after setting a new endurance record of 237 days in space.

The descent of a red-and-white parachute bearing the crew of the Soyuz T11 onto the vast Central Asian plain was shown on the main Soviet television news program tonight. The cosmonauts landed about 500 miles northeast of Tashkent in Kazakhstan at 1:57 p.m. Moscow time, said the official Tass news agency. They looked tired but pleased as they reclined in shaded chairs for interviews by the Soviet press.

The three crew members -- Leonid Kizim, Vladimir Solovyov and the first space physician, Oleg Atkov -- had lived on the Salyut 7 orbiting space station since Feb. 9. In early September they surpassed the 211-day record set last year by another Soviet crew in the same space station.

The Soviet space program has put emphasis on the gradual lengthening of manned flights, with the ultimate goal of establishing large, permanently manned orbiting complexes. This effort has been accompanied by attention to the effects of long-term weightlessness, one of the reasons for including Dr. Atkov, who is a heart specialist.

Atkov regularly checked the cosmonauts during their stay in the space station, Tass said. "New scientific data were obtained, necessary for working out optimal regimes of work and rest for crews on endurance space missions," said the agency.

The Soviet media had indicated in recent weeks that the Salyut crew was growing weary. To save their energy, their working day was cut by one hour. A medical checkup given today after touchdown found the three to be in good health, Tass said.

In a recent interview in the newspaper Socialist Industry, a medical specialist said recent endurance flights showed humans can live in space a year or more. The U.S. endurance record is 84 days set by three astronauts in a mission ending in 1974.

Sen. Spark Matsunaga (D-Hawaii), sponsor of a bill seeking renewal of the U.S.-Soviet Space Cooperation Agreement that expired in 1982, cited scientific opinion that the Soviets' ultimate objective is a flight to Mars. "Why don't we do it together?" he asked. "I have proposed a program of joint U.S.-Soviet missions of gradually increasing complexity, building toward a joint manned mission to Mars in the 21st century."

In television interviews, the cosmonauts said they were glad to be back with friends on the "warm Earth," although one said he was sad to leave the empty space station behind.

All three cosmonauts were awarded medals by the Presidium of the Supreme Soviet upon their return. Kizim, who headed a crew that linked up with an earlier space station in 1980, will be honored with a bronze bust, Tass said.

The crew's imminent return was announced yesterday. The cosmonauts spent their last days on board transferring material to their spacecraft and "mothballing" scientific equipment on the Salyut. The space station, launched in April 1982, will continue in orbit.

During the 34-week stay, Kizim and Solovyov made a record six space walks and spent almost 23 hours outside their capsule. They were joined twice by visiting crews. One in April included Indian astronaut Rakesh Sharma and another in July brought Soviet cosmonaut Svetlaya Savitskaya, who became the first woman to walk in space.

The crew conducted scientific tests on the effects of weightlessness on structural materials and experiments for obtaining super-pure biologically active substances and medical preparations, Tass reported.

The Soviets launched their first orbital station in 1971. The sixth, the Salyut 6, stayed in space almost five years, carrying five host crews and 11 guest crews. The stations are supplied by Progress cargo ships that can carry more than two tons of fuel, food, air and research equipment.

Soviet crews twice had problems reaching Salyut 7. In April 1983 the Soyuz T8 spacecraft had trouble docking at the space station and was forced to return to Earth. That tense event was reported in the Soviet press, but no mention was made of a September 1983 mission that Soviet officials privately confirmed was aborted when a booster rocket exploded on a launch pad, injuring three cosmonauts.