LISBON, JULY 20 -- Prime Minister Anibal Cavaco Silva's sweeping triumph in yesterday's election indicates Portugal has gained enough confidence in its democracy to entrust governmental power to a single party, according to observers here.

Since leftist Army captains toppled Western Europe's oldest dictatorship in 1974, voters have elected a series of incompatible coalitions and weak minority governments in what political analysts saw as an attempt to check political power.

But after 13 years of damaging government crises, Cavaco Silva apparently has inspired sufficient national confidence to secure an unprecedented parliamentary majority for his center-right Social Democrats.

"His victory marks the start of a new era," said a prominent left-wing commentator. "Portugal is beginning to overcome the trauma of the dictatorship and lay to rest the ghosts that have made us wary of strong leaders."

Cavaco Silva's majority enables him to begin reforms -- blocked by the left-wing majority in the last parliament -- aimed at liberalizing Portugal's state-dominated economy. A priority is revising e Socialist-inspired 1975 constitution so that Cavaco Silva can begin streamlining the huge, deficit-incurring public sector.

He has said he also will promote private ownership over collectivization in agriculture, easing the bureaucratic burden and modernizing industry to enable Portugal to reap the greatest benefit from its membership in the European Community.

Cavaco Silva is the most prominent of a new generation of academics and economics specialists who are coming to the forefront of Portuguese politics to replace the lawyers and veteran politicians, personified by Socialist President Mario Soares, who began their careers in clandestine opposition before 1974.

An economics professor who served briefly as finance minister in 1980, Cavaco Silva, 48, rose two years ago to win control of the then deeply divided Social Democratic Party. He provoked the collapse of the governing Social Democratic-Socialist coalition and came out of the ensuing election at the head of a minority government, uniting the party behind him.

According to news reports, Cavaco Silva immediately halted the clandestine shipment of U.S. arms from Israel to Iran via Portugal when he came to office in November 1985. The previous government allegedly had allowed them.

Although staunchly committed to the North Atlantic Treaty Organization, Cavaco Silva has shown a determination to win more U.S. aid in return for American use of military facilities on the Azores islands and is expected to drive a hard bargain if Washington seeks to transfer a U.S. F16 squadron from Spain to southern Portugal.

The premier's serious-minded, plain-talking approach to government has won him support in a country where party infighting has dominated political life and successive crises have stunted economic growth. But opponents criticize him as haughty and unbending.