For the first time, high officials of the Chilean government including representatives of the regular national police, have testified in court that national security police have been responsible for the mysterious disappearance of persons in Chile.

Until now the government has taken the position that the security police, known as DINA (National Intelligence Directorate) have not been connected with the disappearance of hundreds of persons who have vanished since a military junta took power in this country in a 1973 coup.

The government has contended that the issue of missing persons is a fabrication and part of a campaign led by the Soviet Union to discredit the military government that ousted the leftist administration of Salvador Allende four years ago.

The testimony by government officials that DINA has been involved in the disappearance of two men - one of them missing for 18 months - came as sources in the Roman Catholic human rights movement reported that a new round of detentions by DINA began about six weeks ago and that some of the 45 persons arrested so far are still missing.

In the past, such DINA roundups have lasted at least five months and have involved hundreds of arrests and alleged disappearances, according to data from human rights organizations. A period of arrests has characterically followed by a lull, such as from January to March of this year, when there were no disappearances and few arrests.

The evidence of DINA involvement is missing persons came in testimony in Chilean courts on the disappearance of two men - Alejandro Avalos Davidson, a researcher at Catholic University missing since November 1975, and Carlos Contreras Maluje, a pharmacy employee allegedly arrested in November 1976.

Retired Adm. Gorge Swett, the goverment-appointed rector of Chile's Catholic University, said in sworn testimoney that two men who identified themselves as DINA agents came to his office on Nov. 3, 1975, to request information on Avalos, then 30.

Avalos disappeared on his way home from work Nov. 20 and was seen inside DINA interrogation centers until February 1976, according to court testimony by three fellow prisoners who were later released.

Two other university officials, one of them Swett's private secretary, testified that DISA agents had informed the university that they intended to arrest Avalas. The secretary, Carlos Bombal, said he told Swett that agents had told him they had orders to arrest Avalas "without witnesses," but Swett said in a later statement to the court that he did not recall being told that.

The government has denied Avalos' arrest on numerous occasions, including in replies to the courts and to the British embassy. Avalos' mother is a British subject.

In the second disappearance, Capt. Clemente Nicolas Burgos of the National Police (carabineros) testified in court that he saw Contreras, a former communist-elected municipal official in Concepcion, taken into custody by DINA agents on Nov. 3 in central Santiago.

Burgos, who also testified he had been ordered by his superiors not to mention DINA's role to the court, told a chilling story of how Contreras attempted suicide to avoid being arrested by DINA.

The police captain said Contreras had thrown himself in front of a bus and was on the ground bleeding when the officers arrived in a patrol jeep. Contreras cried out that he wanted to die because he was being chased by DINA agents, Burgos testified. While awaiting an ambulance he had summoned for Contreras, Burgos said, men drove up in an auto, identified, themselves to the police captain as DINA agents, forced Contreras into the car and drove away. Contreras has not been seen since.

An appeals court in January ordered the Interior Ministry to release Contreras, but the ministry gave the usual answer that the person in question was not in custody. The Chilean Supreme Court has ordered an investigation of the incident continued.

Catholic Church sources said the new wave of arrests began in April and gained momentum in the first half of May. Court petitions claim that a number of those arrested were kidnaped from their homes at night, held for a few days in secret interrogation centers, then released.

Some of those released reported they had been brutally beaten and tortured with electricity during interrogation, human rights sources said.

The latest group of arrested persons reportedly includes members of the Socialist and Christian Democratic parties, union leaders and community leaders who were active in neighborhood organizations during the Allende government.

One such community leader, Williams Zuleta Mora, 35, who worked in a settlement in the town of Maipu, alleged was abducted by four men and taken to a house in south Santiago where he was beaten and tortured.

Zuleta escaped to his home. Several days later an ambulance arrived and attendants said they had been sent by Zuleta's employer to take him to a hospital. Zuleta's sister-in-law was allowed to ride in the ambulance, but was pushed out a few blocks away. Zuleta has not been seen since.

The new round of arrests appears to be similar to four previous periods of repression in Chile that have occurred since the coup. Records of human rights groups show the first lasted from December 1973 to March 1974 (180 missing), July 1974 to February 1975 (390 missing), August to December 1975 (178 missing), and April to September 1976 (101 missing).