The detention here this week of a former Gestapo officer who is accused of supervising the murder of more than a million people in Nazi concentration camps during World War II has revived again the charge that fugitive Nazi war criminals continue to use South America - and Brazil in particular - as a convenient hiding place.

Gustav Franz Wagner, 67, a former concentration camp officer who has been living in Brazil under his own name since 1950, was placed under preventative custody" Tuesday after turning himself over to Brazilian authorities. Accusations against him first appeared in the Brazilian press last week.

Wagner's detention followed a dramatic confrontation at the Sao Paulo headquarters of Brazil's feared political police in which Wagner was identified by Stanislaw Szmajnzer, a jewish concentration camp survivor.Szmajner said his life once was spared by Wagner, who he described as having been second in commandat the notorious Sobibor concentration camp in Poland in 1942-43. Szmajner also said Wagner "sent most of my family to death" at the camp.

"Smajner has made a positive identification, and after meeting with Wagner this morning, the German consul told me that 'this is definitely the man we've been looking for.'" said police chief Silvio Pereira Machado. "That is more than enough evidence to hold him in custody until the formal extradition requests arrive."

Austria, where Wagner was born, has already requested extradition and the West German embassy said it will also. Wagner has been wanted on war crime charges by the Bonn government for years. According to police sources here, an extradition request from Poland, on whose territory Wagner served, is also expected. Israel act, because it has no extradition treaty with Brazil.

Discovery of Wagner comes little more than a decade after Franz Paul Stangl, Wagner's commander at Sobibor and also head of the Treblinka camp, was found working at a German-owned factory in Sao Paulo, Stangl was extradited to West Germany and convicted. He died in a Germany prison.

Wagnr has been accused by the Vienna-based Nazi hunter Simon Wesisenthal of having supervised the day-to-day extermination of more than a million people and of having personally killed uncounted thousands of prisoners. According to Wesienthal. Wagner was known to camp inmates as "The human beast" and "is just important as Adolf Eichmann and Joseph Mengele."

Eichmann was kidnapped in Argentina in 1961 and tried and executed in Israel. Mengele, known as the "Angel of Death" for alleged medical experiments on prisoners at Auschwitz, is reported to be still residing in Paraguay. A recent Amnesty International report named him as the "technical adviser" to a government program that it described as designed to exterminate Paraguayan Indians.

Wiesenthal, has charge that "there are hundreds of Nazis loose in Brazil" and that such German companies operating here at Volkswagen, Siemans and Krupp "have entire nests of these people."

However, Wiesenthal has not back the charge with public evidence. Volkswagen has denied it.

West German publications for years have sent investigative reporters to South America in search of war criminals with little result.

Brazilian fears of a resurgence of Nazi activity on their soil first surfaced in April in Itatiala, a quiet mountain resort town north of Rio de Janeiro, after an anonymous informant noted red flags and a large number of foreigners at a hotel owned by a German immigrant and told police that a group of "comunists" were holding a secret meeting.

When police and press arrived on the scene, they found that five neo-Nazi groups from Brazil, West Germany, Argentina and Britain were meeting to celebrate Adolf Hitler's 89th birthday. Against their wishes, the hotel's guests were photographed and interrogated and Nazi literature and paraphernalia were seized.

After a Brazilian newspaper reporter took the photos to Wesienthal in Vienna, an unofficial search began. The man who surrendered to authorities Tuesday, saying that he feared for his safety admits that he served in the two notorious Nazi secret police arms, SS and the Gestapo and that he worked in a supervisory capacity at Sobibor. His birth date and other personal data match those contained in the files in the possession of Wiesenthal and the West German government.

Wagner denied having a major role at the camp in Poland, admitting only to being a sergeant assigned to a crew building barracks.

In a press conference at police headquarters, Wagner said that he arrived in Brazil with "safe conduct" papers after a long voyage by ship from Syria in the company of Stangl. According to Wagner, his passage from Europe to Syria and from Syria to Brazil was paid by other Geman Refugees in Syria.