The convincing reelection of President Ramalho Eanes has halted the rightward trend in Portugal that was personified in the confrontation politics of late premier Francisco Sa Carneiro. In the wake of the premier's death in a plane crash, the vote appeared to vindicate Eanes' commitment to consensus policies.

Sa Carneiro's conservative Democratic Alliance government, bereft of its forceful leader and with its presidential candidate routed, resigned Dec. 8, just two months after it won a landslide parliamentary election victory and the day after the presidential defeat. Final results of presidential election gave Eanes 56 percent of the vote and 40 percent ot the rightist candidate Antonio Soares Carneiro (no relation to the late premier).

Subsequently, the alliance nominated Francisco Pinto Balsemao, 43, a cofounder with Sa Carneiro of the Social Democratic Party, to head the next government. Lacking Sa Carneiro's charisma, Pinto Balsemao is considered a moderate in the party who can work comfortably with Eanes. His formal designation may come Monday.

Acting Premier Diogo Freitas do Amaral, a Christian Democrat who took on the job after Sa Carneiro was killed Dec. 4, has played a caretaker executive awaiting Eanes' acceptance of a Cabinet to be presented by Pinto Balsemao.

The late premier had turned the presidential vote into a personal contest by threatening to resign if Eanes were reelected. On his death, the electorate opted for moderation and continuity. A significant slice of the Democratric Alliance switched its rightist vote to Eanes.

At issue in the often vitriolic split between the late premier and the president were not only personal animosities but also differing conceptions about where real power lies in Portugal and about the fundamental electoral basis for governing a country where the military overthrew a right-wing dictatorship less than seven years ago.

Eanes believes in presidential power with its constitutional rights to veto legislation and choose wht premier. Sa Carneiro held that the premier should be the executive strongman. He wanted to curtail presidential prerogatives. Eanes opted for the center while Sa Carneiro passionately advocated right-wing policies to overhaul the leftist legislation that followed the 1974 "Revolution of the Carnations."

Politically there is little to separate Eanes from the mainstream of the Democratic Alliance coalition. He favors expunging the Marxist phraseology built into the constitution just after the revolution. He would end the institutional role of the military as watchdogs of the constitution. Eanes backs continued close ties with NATO and an early entry into the European common Market.

Eanes is widely respected as the general who put an end to revolutionary excesses spearheaded by the Communist Party in 1975. He was opposed by the Communists and supported by Sa Carneiro in the 1976 presidential election. This time the leftists supported his as the lesser evil since they had branded the Democratic Alliance candidate a fascist.

Former premier Mario Soares has formally reassumed the post of secretary general of the Socialist Party after resigning in October over his party's support for the Eanes presidential candidacy. A Socialist Party congress, scheduled for March, is expected to remove Soares from that chief party executive job, reflecting the political erosion that the onetime key figure of national politics has undergone and paving the way for new government pacts. o