Chilean police this morning broke up a peaceful protest vigil in a busy central plaza by about 100 person who had pinned to their clothes pictures of political prisoners who allegedly have disappeared. Forty of the protesters and several bystanders including an American journalist were detained.

Today's incident was the first time dissenters have staged a protest in a public street since a coup four years [WORD ILLEGIBLE] an anti-Communist military government that has banned all political parties and public demonstrations.

The protest, in a plaza outside the Chilean Foreign Ministry located in La Moneda palace, the former government headquarters, ended just as new U.S. Ambassador George W. Landau arrived for his first meeting with Chilean Foreign Minister Patricio Carvajal. Embassy sources said Landau did not notice the protesters, who were being loaded in police vans about 60 yards from the entrance to the Foreign Ministry.

The protesters, mostly women, are members of a group called Relatives of Disappeared Prisoners, formed two years ago to use legal action and complaints to international human rights organizations to support their demand that the Chilean government clear up the fate of 566 persons they say vanished after arrest by security forces. In July, 26 members staged a 10-day sit-in and hunger strike in the Santiago headquarters of the United Nations Economic Commission for Latin America.

The government said in a recent statement to United Nations that there are no political prisoners now held without trial in Chile. In an official response to U.N. Secretary General Kurt Waldheim last month, the Chilean Foreign Ministry said the missing relatives of the 26 hunger strikers were not in custody.

Maria Teresa Barahona, who wore a picture of her missing husband, Communist Party youth leader Jose Weibel, in today's protest, said afterward that the action was directed to the U.N. General Assembly rather than to attract the attention of Landau, who arrived in Santiago yesterday.

The top embassy post had been vacant for six months.

The protesters were charged with disorderly conduct, and most had been released by late afternoon. Charles Padilla, United Press International bureau chief, who was taking photographs of the demonstration was taken to a police station with the protesters, but released an hour later after police checked his press credentials.