Leftist leaders, apparently losing patience with the tactics of more moderate opposition groups, are calling for a new offensive aimed at ousting authoritarian ruler President Augusto Pinochet.

Clodomiro Almeyda, a Socialist Party leader released last week after more than a year in prison, told the first leftist rally since the Oct. 5 plebiscite it was time "for the people to take the offensive."Pinochet was defeated in the plebiscite, which offered Chileans a chance to vote "yes" or "no" to another eight years of his authoritarian rule.

"We will not permit the dictator, politically defeated in the plebiscite, to recover and take the initiative," said Almeyda, a Cabinet minister under Salvador Allende, the Socialist president who died in the Sept. 11, 1973, coup that put Pinochet in power.

Almeyda spent 12 years in exile before returning to Chile secretly in March of 1987, when he was arrested and jailed.

Pinochet's defeat clears the way for an open presidential election now set for December 1989.

Anibal Palma, a leader of the United Left coalition and president of the Radical Democratic Socialist Party, told the Sunday rally the "opposition must mobilize now, taking advantage of the strong position given it by the victory." Pinochet, he said, "must not be given time to recover."