A decisive victory

IN winning an absolute majority in Portugal's parliament, Prime Minister Anibal Cava,co Silva's Social Democrats are now in position to bring a new period of political stability to the strategically important European nation. The victory also ensures continued close economic and defense ties with the European Community and the United States. Mr. Cava,co Silva has steered his nation along a centrist-to-conservative economic course, no small achievement in a society where leftist political parties abound and - until this weekend's election - have shown clout at the ballot box. The opposition Socialist Party barely held its own in parliament. Other parties of the right and left, including the Communists, suffered sharp losses.

In the last parliamentary election, in 1985, Cava,co Silva's Social Democrats won 29 percent of the vote, well below this weekend's apparent 51 percent. Earlier this year, Cava,co Silva lost a censure vote sponsored by a left-wing party, which precipitated this election.

In this election Cava,co Silva campaigned on a call for political and economic stability, pointing to a relatively strong economy. The strategy worked.

Cava,co Silva will now push ahead with constitutional revisions (Portugal's Constitution was drafted with Marxist economic principles in 1974). He wants greater legal recognition of market-oriented economic policies, structural reforms for Portuguese industries, and a shrinking of the public sector. He must address economic problems stemming from Portugal's entry into the European Community. Fortunately, he can expect support from the more conservative wing of the Socialist Party.

Portugal has proved a close ally of the US. Both Lisbon and the Pentagon have hinted that in case of forced US troop reductions in Spain, Portugal might offer an alternative basing site.

Neither side ought to appear in a hurry to promote this prospect.

Under Cava,co Silva, Portugal is advancing toward political and economic stability - which controversy over troops and facilities would not help.