Spain's civilians harder on plotters than the military

''Now Spanish society can feel peaceful because this chapter has been closed for all.'' Prime Minister Felipe Gonzalez was referring to the decision by Spain's Supreme Court to increase the sentences imposed earlier by a military court on the main participants in the foiled coup attempt of February 1981.

The civilian court overruled the original sentences dealt out last June by the Supreme Council of Military Justice.

Many Spaniards had considered most military sentences shamefully lenient. But the president of the military court, Lt. Gen. Manuel Esquivias Franco, defended them, saying he was surprised at the ''very harsh'' new sentences. He added, however, that the Supreme Court and his court had each ''acted according to its conscience.'' And he insisted that ''the sentence will be obeyed, independently of the fact that it seems harsh to us.''

The military court had totally absolved 11 lieutenants and handed out light two-to-five-year sentences for the majority. The man whom the plotters intended to become the head of government if the coup succeeded, Gen. Alfonso Armada, received only a six-year sentence widely considered disgraceful.

The Supreme Court increased 12 of the 22 military sentences. It gave one-to-two-year sentences to eight of the 11 lieutenants who had been absolved even though several of them were well identified in television playbacks roughing up Spain's then Defense Minister Gen. Gutierrez Mellado.

What has produced the most popular satisfaction here, however, has been the upgrading of Gen. Armada's six-year sentence for conspiracy to the maximum 30 years for military rebellion. This places him in the same category as Gen. Jaime Milans dKl Bosch, whose forces seized control of Valencia, and Lt. Col. Antonio Tejero Molina, who held the entire government and parliament hostage at the hands of his machine gun armed civil guards for more than 18 hours.

The reaction from civilians has been favorable. Politicians across the political spectrum welcomed the Supreme Court's ruling.

Military spokesmen have made no comment or have limited remarks to a support of the constitution, and the decision of the Supreme Court.

''Justice is justice,'' said the chief of the Civil Guard, Gen. Jose Aramburu Topete, who played a major role in helping to thwart the coup, ''and what the court does is well done.'' Some Spanish papers mention the possibility that the stiffened sentences may act as a catalyst for coup plotting sectors of the armed forces that have been keeping a low profile since the Socialists took office.

But most Spaniards are hoping that Spain's young democracy is now firmly established after weathering both this coup attempt and a plot scheduled for last Oct. 27.