Bolivian President Hugo Banzer moved yesterday to crush a growing, 20-day-old hunger strike by more than 1,200 persons seeking release of the South American country's political prisoners and permission for thousands of political exiles to return.

According to reports reaching Washington, approximately 600 strikers were arrested in La Paz, Bolivia's capital. As word of the early morning arrests spread through the country, students took to the streets of La Paz in protest and tin miners called a 48-hour work stoppage in support of the hunger strikers.

Jaime Ponce Cabellero, leader of the normally pro-government Bolivian Socialist Falange, reportedly condemned the arrests and called for Gen. Banzer's resignation. According to the reports, the Bolivian government had been negotiating with the strikers as late as Monday evening.

At 11 that night, however, the government abruptly changed course and warned the strike leaders in La Paz that they had one hour to end the protest and go home. The arrests began shortly after midnight and reportedly included three Roman Catholic nuns and three priests.

The hunger strike began Dec. 29, a week after Banzer announced a limited amnesty for exiles whom the government had banished for political or union activities. Many prominent exiles, including former President Hernan Siles Suazo, were listed as ineligible for return under terms of the amnesty decree.

About 20 wives and children of several union leaders who were also not covered by the amnesty decree began the hunger strike, which continued to grow.

Students, religious leaders, journalists and workers reportedly joined in seeking a blanket amnesty for detained or exiled citizens. One of the strikers' arguments was that national elections - scheduled by Banzer for July - could not be legitimate if opposition leaders were kept out of the country.

The State Department had no official comment on the Bolivian developments, but officials at the Washington Office on Latin America, a church-supported human rights group, said the U.S. embassy in La Paz has been helping observers sent by the World Council of Churches, the National Council of Churches and the U.S. Catholic Conference in meeting with Bolivian government officials.

Sources in Washington said the official U.S. position could hinge on how the arrested strikers were treated.

Rep. Donald M. Fraser (D-Minn.) issued a statement saying he hoped the Bolivian government would reach an agreement with the strikers that "would respect the right of the miners and other opposition elements in Bolivia."