Italy hardly ranks among the economic giants of the world. Yet Italian firms are among the most technologically advanced on earth, and they are coming up with new developments that are contributing to industrial progress in other nations, including the United States.

In many ways, the technological innovations being perfected here are a direct response to the fact that Italy's weak economy needs fresh ideas to keep it going.

The country's enormous reliance on imported oil, for example, has been spurring Italian technicians toward research into solar energy.

Ansaldo, an electrical engineering company, recently was awarded a contract by the International Energy Authority to construct Europe's first sun-operated power station, to be located in the Spanish town of Almeria. Ansaldo scientists did much of their research on the project at the University of Genoa.

Another large industrial corporation, Montedison, is involved in solar cell technology, and it is building an experimental photovoltaic plant for the European Economic Community.

Montedison has just joined with Solarex, an American company, to develop the technology to manufacture silicon, the main component in solar cells. A factory is scheduled to be built in Italy, and Montedison executives predict that the cost of producing silicon will drop dramatically in the years ahead.

Yet another deal has been signed by SMI, an Italian metallurgical firm, and the Carrier Corp., a U.S. company, for joint research in adapting solar energy to heating systems.

MEANWHILE, Italian outfits are engaged in the quest for other sources of energy. Pirelli, the tire manufacturer, is working under contract to the U.S. Energy Research and Development Authority to study ocean thermal energy conversion, through which energy can be generated by exploiting the temperature differences between the surface and the depth of the sea.

The Italians are moving ahead in nuclear energy, too. Italy owns a 25 percent interest in Eurodif, the multinational nuclear complex that is one of the world's largest producers of enriched uranium. Fiat, the Italian automobile firm, recently reached an agreement with Ingersoll Rand, the U.S. company, to develop nuclear pumps.

Italian companies have been less successful than other firms in oil exploration. But Italian outfits turn out sophisticated oil drilling, pumping and refining equipment, and one of them, Samprogetti, not long ago won a $500 million contract from both Texaco and Gulf to enlarge their British refineries.

The high price of gasoline here has also inspired Italian automobile manufacturers to study ways of producing lighter cars that consume less fuel, and this has led to advanced aluminum cast technology. Fiat, which has put up the only aluminum foundry in the world, will soon begin to supply aluminum engine parts to Ford and Chrysler.

Troubled by labor unions, which refuse to allow workers to switch assembly lines, Fiat has developed an electronic system to overcome the problem. Known as Robogate, it permits different automobile models to be assembled on the same line, with sensors serving to direct various operations. A Robogate system has just been purchased by Chrysler.

Unable to compete on a global scale in the aircraft industry, Italy has chosen to produce components for foreign companies, and the strategy has paid off.

THE BIGGEST Italian airplane manufacturer, Aeritalia, is building parts here in Italy for the new Boeing 767, and the firm is under contract to produce elements of the fuselage for the DC-93/880, the latest McDonnell Douglas model.

Deals for the production of aircraft engines also have been signed recently by Fiat and Pratt and Whitney as well as by Alfa Romeo and General Electric. A consortium of French, British, West German and Italian firms is constructing the Tornado fighter-bomber for the North Atlantic Treaty Organization.

Excluded from the strategic arms race because of limited resources, Italy has concentrated on designing and producing relatively inexpensive conventional weapons, and this approach has been successful. These weapons include land-to-sea missiles, field howitzers and training aircraft, and they have pushed Italy to fourth place among the world's exporters of arms.

All this should serve as a reminder of the fact that Italy has long been in the forefront in the development of new technology ranging from automobiles and motor scooters to typewriters and radios. And it proves as well that a country can, despite political and economic difficulties, continue to demonstrate unique ingenuity.