MOSCOW, DEC. 29 -- Soviet cosmonaut Yuri Romanenko, the world's most experienced space traveler, returned to Earth today with two colleagues after a record 326 days, crowning a year of achievements for the Soviet space program.

Covered live on Soviet television, the touchdown of the Soyuz TM3 space capsule on the snow-covered steppes of Soviet Kazakhstan was met at the Soviet space control center by broad smiles and hands clasped in victory signs.

Romanenko, 43, was shown on the evening TV news coming out of the capsule into a snowstorm and telling reporters, "I feel great. I'm satisfied with the work I did and glad to see you on the earth of Kazakhstan."

"A new achievement of the Soviet space program," announced a headline in the government evening newspaper Izvestia.

Romanenko surpassed the previous 237-day record for space endurance, also set by a Soviet crew, on Oct. 1. According to some reports, he had been feeling homesick in the cramped quarters aboard the Soviet space station, known as Mir, or peace.

The Soviet space program in recent years has put priority on prolonged exposure to weightlessness and other conditions in space. One goal is a manned flight to Mars, planned for early in the next century, which scientists estimate would last more than 30 months.

Alexander Alexandrov, 44, one of the two cosmonauts who returned with Romanenko, came back after 160 days in space. The third, Anatoly Levchenko, 46, arrived at the space station only last week to help prepare for a crew changeover.

Two other cosmonauts, Vladimir Titov, 40, and Musa Manarov, 36, were left behind on the Mir and are now expected to stay in space for a year, according to the Soviet news agency Tass.

The crew switch aboard the Mir signaled the start of a permanently manned space station, another goal of the Soviet space program and the principal purpose of the Mir, a hub equipped with docking stations launched in February 1986 in honor of the 27th congress of the Soviet Communist Party.

Romanenko, a veteran cosmonaut who spent New Year's Day 1978 in space, took off on his mission in February this year with Alexander Laveikin. Laveikin had to return to Earth in July because of irregularities in his heartbeat.

The return today took three hours, according to Soviet television, which showed the five cosmonauts on board the Mir bidding one another farewell. Upon their return, Romanenko and Alexandrov were greeted by their families, while Levchenko went on immediately to flight tests connected with the Soviet space shuttle program.

According to a report in this evening's Izvestia, relations between the cosmonauts and their ground controllers were getting testy during the last days of their mission. One of the cosmonauts complained that they were spinning in space "like squirrels in a cage" and sniped at ground control to stop nagging, the newspaper said.

Tass said the returning crew brought back a mass of scientific data, much of it accumulated on the astrophysics research module Kvant, which joined the Mir station this year.

Kvant's telescopes were the first in the world to record the X-ray radiation of the supernova in the large Magellanic cloud, Tass said. In all, the cosmonauts brought back 270 photographs of space taken by the Glazar ultraviolet telescope.

The Soviets announced this spring that they are planning to send a series of unmanned spacecraft to Mars by the end of the 1990s, launching 30 tons of scientific instruments, support equipment and automated rovers to roam the planet's surface.

In May, the Soviets launched a powerful new rocket capable of hoisting a 100-ton payload into space in what was viewed as the first successful public test of their space shuttle program. The rocket, called the Energia, is the most powerful in the world since the United States discontinued production of the Saturn V rockets.

According to Tass, Levchenko, one of the cosmonauts who returned today, went into space to collect "data necessary to learn to control a reusable spacecraft being built in the Soviet Union." The Soviet shuttle is expected to be ready for launching sometime in 1988.

The string of Soviet successes has shown up in sharp relief the setbacks suffered by the American space program since the January 1986 Challenger disaster. The Soviets have further opened their program to foreign investment this year, offering to launch western experiments and communication satellites into space.

The endurance tests in space have produced a wealth of evidence about the effects of weightlessness on the human body. Tass reported today that Romanenko was able to endure the long flight in space thanks to "a series of disease-prevention measures."

{The development of irritability and "cabin fever" among crew members living for months in the close quarters of a spacecraft is a concern often mentioned in discussions of an eventual trip to Mars, Washington Post staff writer Susan Okie reported. Long stays in space also have medical consequences. Released from the constant demands of supporting the body against gravity, the muscles begin to atrophy -- a problem reportedly experienced by the Soviet cosmonauts despite two hours a day of exercise on a treadmill and stationary bicycle.

{The bones also progressively lose calcium, reducing their rigidity and making them vulnerable to fractures when an astronaut returns to Earth's gravity. In addition, scientists have noted subtle changes in the immune systems of astronauts who spent long periods in space and have expressed concern about the effects of radiation exposure incurred during the time spent outside the protective shield of the atmosphere.}

In an article in Pravda in December, Romanenko told ground control that his calf muscles had shriveled up during the long flight, even though he and Alexandrov, who joined him in July, worked out on the treadmill and bicycle. Soviet TV showed both men having to be helped to a waiting helicopter after today's landing.

In the Pravda article, Romanenko jokingly described how a future spaceman should look to cope with the environment of space: "a bald head, to avoid haircuts," "big arms . . . six would be better," and "slim legs . . . or just one . . . with grips, to keep steady."