MASAYA, NICARAGUA, FEB. 10 -- Maria Oliu, wringing her hands in her apron, was recounting to a reporter yesterday how Sandinista State Security police had charged into her adobe home the night before and dragged away her son, Luis Useda.

The trappings of working-class poverty surrounded her on the dirt-floor patio: a scrawny chicken, a broken wooden chair, several barefoot children with grimy faces. Only a few minutes earlier a gang of several dozen rowdy Sandinista party followers stood outside her front door yelling progovernment slogans and demanding, "Luis to the firing squad!"

As Oliu nervously told her story, three Sandinista State Security vehicles packed with police agents stopped at another modest house just down the street. When the policemen emerged 10 minutes later, the street was filled with neighbors indignant over what they believed was another arrest.

But an aging housewife dressed in an apron much like Oliu's came out to explain that her son-in-law was a State Security agent and had simply stopped off at home for a cold drink.

Monday night's riot in Masaya, which started with a mothers' protest against a military conscription drive, was one of the most forceful antigovernment urban uprisings in Nicaragua since an August 1982 riot in this same city that left two Sandinistas and one opposition activist dead.

A decade ago, residents of Masaya were among first to go into the streets to support the Sandinistas' revolt against dictator Anastasio Somoza.

Since Nicaraguan President Daniel Ortega lifted a state of emergency more than two weeks ago, as a concession to a Central American peace plan calling for democratic reforms, street protests by government opponents have become bolder.

The riot exposed the political polarization wrought by the eight-year-old Sandinista revolution, showing how the rift has divided generations and social classes, pitting mothers against mothers, youth against youth, poor against poor.

In Masaya, 20 miles south of Managua, the tension remained high last night and today, as the Sandinista government mobilized all the resources of its security apparatus and its party to quell the disturbance. Dozens of police, including reinforcements from Managua, patrolled the town.

They continued to arrest suspected opposition demonstrators on the streets and in their homes. A woman passer-by, apparently unaware of the turmoil, was seized as reporters watched in front of the police station yesterday afternoon.

The Interior Ministry, which is in charge of the State Security police, declined to release figures on the number of arrests, but named 13 Nicaraguans, most of them members of opposition political parties, who were charged with instigating the riot. Useda, a lay Roman Catholic activist and leader of the Social Democratic Party, was named by police as an organizer. His mother said he was at home when opposition demonstrators burned two cars and stoned the police station and a Sandinista Youth center Monday night.

Opposition sources said there had been at least 20 arrests.

Late yesterday, the Sandinista National Liberation Front, the ruling party, summoned its sympathizers to a march to demonstrate its power over the streets, but fewer than 1,000 Sandinistas showed up.

In the evening, antigovernment protesters lit a giant bonfire with car tires in Monimbo, a militant opposition neighborhood that had once been equally militant in its opposition to Somoza. At about 9 p.m. dozens of police arrived to disperse the crowd, swinging clubs.

Because Sandinista organizations reach across class and social lines, the leftist government was able to restore control even in Masaya, where it is widely loathed.

Many street marchers who turned out for the Sandinista rally were from poor families of Sandinista soldiers killed in action or working-class youths who had already done their obligatory two-year service under a conscription law imposed in 1983.

One militant, student Alcides Altamirano, waded into a knot of opposition parents yesterday to "clarify the situation for them." He ended up in a shouting match with a working-class mother, Rosa Emilia Nicolas.

Nicolas, waving her son's birth certificate, said he is two years underage for the draft but has been grabbed twice for Army conscription. Altamirano yelled back that the draft is compulsory by law in Nicaragua and the mothers should remember the thousands of drafted youths who have given their lives fighting U.S.-backed rebels.