In the cold refracted light that bathes the cavernous laboratory of spotless tile and glass, the scene looks like a set from the latest George Lukas space extravaganza.

In an atmosphere purified to 100,000 times that of the normal air outdoors, the giant cylindrical body of a future U.S. National Aeronautics and Space Administration manned space laboratory sits on a cradle of tubular steel as white-smocked technicians pad about, crating a flat, mirrored satellite recently assembled for a European space program.

Behind a wall of thick glass, where banks of computers wink with red and green lights, another group of technicians sits in the luminous green glow of a bank of monitors, running program tests on components for another satellite soon to be assembled here.

The vast high-tech chamber is the "integration room" of Aeritalia's space systems plant on the outskirts of this auto-making capital of Italy. It represents the cutting edge of a budding Italian space industry whose leaders are increasingly eager for their government to give the go-ahead to official Italian participation in President Reagan's Strategic Defense Initiative, the space-based antimissile program popularly known as "Star Wars."

Italy, like West Germany and Britain, has been edging toward participation in the $26 billion, five-year U.S. program. But, because of Italy's large Communist Party, Prime Minister Bettino Craxi's two-year-old Socialist-led coalition has put off committing the Italian government to official cooperation with the U.S. space initiative.

"It is my belief that the Italian government supports SDI," Ernesto Vallerani, the head of Aeritalia's Space Systems Division, said in an interview here, "although the government has not acted politically on it yet."

"I see no signs except positive ones about Italy's participation, although of course politics could still interfere," said Vallerani, an Italian-trained aeronautical engineer whose company participated in building the shuttle-orbited spacelab for NASA and is cooperating on four other space projects with the U.S. agency. "All the signs we have received from the government are in line with a positive response."

Italian government officials close to negotiations with the United States on SDI cooperation privately agree that the Craxi government is in favor of an official commitment to participate in the program. But these sources said Craxi was still unsure when and how to announce the decision because of uncertainty of its impact on the volatile Italian political system.

It is the political wisdom here that any decision by the government to go along with Reagan's SDI will be opposed by Italy's powerful Communist Party because of the program's military and strategic implications. The Communist Party is supported by about 30 percent of the electorate.

Even so, negotiations between the U.S. and Italian governments began in August, when Lt. Gen. James Abrahamson, the head of the SDI program, visited Italy to explain the program and the areas where Italian industry might cooperate.

More detailed discussions were held in September when Brig. Gen. Malcolm O'Neill, director of the Kinetic Energy Office in the SDI program, headed a five-man U.S. delegation that spent four days here.

O'Neill and his delegation talked to government and industry leaders and toured the facilities of more than a dozen companies that have submitted proposals, ranging from satellites to laser development, for SDI consideration.

Italian and U.S. sources here said the O'Neill team was definitely interested in at least four of the research proposals and was prepared to study 10 others. These sources said that if there was government endorsement that would pave the way for government funding, some contracts could be ready for signing in a matter of months.

Industrialists in Italy's aerospace and defense sector are understood to be pushing for a quick decision. They believe that the Reagan initiative opens vast opportunities for the development of high technology in Europe that are far better, and more immediate, than the French-inspired Eureka plan for inter-European technological cooperation.

Eureka, announced by French President Francois Mitterrand last spring as a European alternative for peaceful technological development to the military SDI program, has yet to gain funding from other European governments.

The debate over whether Italian industry -- and the government -- should participate in Eureka or SDI is one that Italian industrialists, at least, consider academic. They believe they can, and should, do both.

Gianni Agnelli, the chairman of the Fiat auto empire and its related defense industries, said in a recent interview with the International Herald Tribune, "I believe both SDI and Eureka can be done, but we are going ahead with the U.S. program first because it is ready with financing and staff and will start soon."

Two Fiat research proposals are among the four that most interested the O'Neill delegation, according to Italian sources.

Agnelli's managing director at Fiat, Cesare Romiti, went further in a speech this fall terming the European debate about whether it was best to participate in SDI or Eureka as "unhelpful, unfounded and animated only by ignorance and prejudiced ideological distortions." He said that SDI and Eureka are complementary.

Such statements are part of the Italian industrialists' growing campaign to encourage Craxi to take the plunge into SDI so that they can get on with it -- and expand their research and development budgets with, they hope, U.S. investment dollars.

Italian government sources said Craxi was still hoping for some sort of common European response to SDI that would cushion the shock he expects from Italian leftists if the government does go along with SDI.

Discussions are continuing between the British, West Germans and Italians on the issue. Meanwhile, the decision on whether to participate officially in SDI remains in abeyance while the companies that would be involved in it continue planning.

"As a technical man I have only to welcome the fact of SDI even if as a man I may not be overjoyed with the militarization of space," Aeritalia's Vallerani said. "New technology always follows military research and the benefits that can come from that are incalculable. I am already in my mind listing the companies in the United States we can work with, and the projects we might undertake."