LISBON -- Exactly five centuries have gone by since Bartholomeu Dias sailed out of a storm and pulled into Mossel Bay, opening a new era by becoming the first European to round the southern tip of Africa.

The feat, which opened the way to the Indian Ocean and oriental treasures, was a high point in a remarkable series of government-sponsored Portuguese discoveries in the 15th and 16th centuries that have been compared to modern-day space exploration for their organization and impact on science.

Portuguese have just begun a 12-year celebration of that glorious past, seeking inspiration and confidence for what many here feel could be the start of another leap in history after years of stagnation. In the first major observance, President Pieter W. Botha of South Africa joined Portuguese officials last Wednesday at Mossel Bay, about 230 miles east of what is now Cape Town, to mark Dias' historic landing on Feb. 3, 1488.

In simultaneous ceremonies in Lisbon, President Mario Soares declared the commemoration of Portuguese discoveries, scheduled to last until the year 2000, provides "a unique opportunity to unite and mobilize the Portuguese people around the exalting idea of modernity." His remarks, in a speech to the national assembly, reflected a sentiment taking form here that Portugal has shed the backward heritage of its long dictatorship, debilitating colonial wars and a chaotic revolution and finally is ready to start catching up with the rest of Europe.

"There is definitely a feeling that we are starting a new cycle in our history," said Joao Vale de Almeida, who runs the European Economic Commission office in Lisbon.

However accurate these 20th century expectations turn out to be, the Portuguese discoveries definitely marked a great acceleration in Europe's knowledge back then and put this little country at the frontier of science. Portuguese mariners revolutionized cartography, astronomy, geography and shipbuilding as they opened Africa and the Orient to trade with Europe.

"We were great at that time," declared Commander Rodrigues da Costa of the government's National Board for the Celebration of Portuguese Discoveries. "From 1480 to 1520, we were the greatest in the world, no doubt about it."

Celebrations have been scheduled to mark only the major discoveries, such as the African coast, Brazil, India and Japan. Da Costa said marking them all would be too much of an undertaking.

"Argentina, yes, we were first," he recited. "Brazil, yes, we were first. Malacca, yes, we were first. Japan, yes, we were first, and Hormuz, and all up through the Arab emirates. Portuguese were the first Europeans to go there, too, but we don't have the resources to celebrate everything."

The American historian Daniel J. Boorstin, former director of the Library of Congress, wrote in his book "The Discoverers" that Portuguese exploits, in contrast to Columbus' fortuitous discovery of America, were the fruit of methodical planning, government sponsorship and careful accumulation of scientific data. "The Portuguese achievement was the product of a clear purpose, which required heavy national support," Boorstin wrote. "Here was a grand prototype of modern exploration."

In calling special attention to the discoveries through a 12-year program of exhibits and observances, the board has aimed for more than memory. It also is seeking a revival of national pride and the spirit of enterprise.

The 15th and 16th century exploration, experts have said, took place in part because Portugal enjoyed national unity and government stability then while the rest of Europe was torn by strife. Officials here noted that Portugal now appears to have ended a period of its own strife, losing the African colonies and struggling through a tumultuous revolution.

Prime Minister Anibal Cavaco Silva, for example, last July won the first absolute parliamentary majority enjoyed by any government here since the dictatorship fell in 1974. In a message ushering in discovery observances, he urged that the early Portuguese explorers become examples for "the economic and social progress we have to carry out, in the political and institutional stability we are living, to prepare for the coming century."

"All the Portuguese discoveries have for a long time been emblematic for the Portuguese people," Da Costa said. "But now they can be an example and an inspiration for young people, for students and technicians, to move forward. We have lost our empire; now we must discover ourselves."