Police and troops raided neighborhoods and arrested dozens of persons here for the second straight day today as the government of Gen. Augusto Pinochet sought to head off antigovernment protests called for this week.

One day after searching and patrolling at least seven poor and working-class districts on the perimeter of Santiago, thousands of police and troops fanned out across the city again this morning to repeat the operations in some neighborhoods and expand them to others.

In at least two areas of southeastern Santiago, Santa Julia and Lo Hermida, government forces rounded up hundreds of men from the streets and assembled them in community centers for checks of police records. Several of those detained later said those men with police records were taken away on buses.

Security operations also were reported in three other neighborhoods in southern and eastern Santiago. Most of the raids lasted for about two hours, witnesses said. No violence was reported.

Authorities have provided no information on the raids nor on the number of arrests, and Chilean media have not reported on them. Reports from human rights groups, church officials and witnesses indicated that at least 70 persons have been arrested in the two days.

The military activity has been staged before nationwide antigovernment demonstrations called by the opposition for Tuesday and Wednesday to defy the state of siege imposed by President Pinochet Nov. 6. Opposition leaders seek to deal a political blow to the government and preserve their own movements by showing they can disrupt the country even under a government crackdown that has included mass arrests, censorship of all political news from the media and strict limits on freedom of assembly.

Opposition leaders and other observers here said this weekend's military mobilization indicated that the government is planning a major effort to stop the planned two days of demonstrations. Pinochet had not used troops to suppress protests since August 1983, when 27 persons were killed during two days of violent clashes.

In the neighborhoods searched today, many residents said the operations had frightened the population and reduced the chance of a protest. However, said Antonio, a 27-year-old who was picked up in Lo Hermida and held for two hours, "something will happen anyway. People here are always protesting, and they have never been frightened off before."