The article "Singapore Acts to Bar Dissent" {June 15}, by Keith B. Richburg, accusing Prime Minister Lee Kuan Yew's government of "harsh treatment . . . of almost any form of dissent against his rule," contains serious errors and omissions.

The article cites as its main example of repression the arrest of 16 persons by the Singapore government under the Internal Security Act for taking part in a conspiracy to set up a Marxist state. It reported Amnesty International's statement that the 16 were "prisoners of conscience engaged in the non-violent exercise of their beliefs." It did not report the admission of Vincent Chang, a key figure in the plot, that he was a Marxist who had been in contact with Filipino communists; that he was, on instructions, setting up a communist network; that he was consciously infiltrating legitimate organizations, including religious bodies; and that he was building up pressure groups for confrontation with the government, starting with peaceful protests, escalating to mass events, "leading to public disorder and maybe even rioting, bloodshed and violence."

As for confessions having been obtained through coercion, all those arrested have been allowed access to lawyers, relatives and the prison chaplain. None has complained of torture or ill-treatment.

The article also did not report the public statements of the archbishop and other Catholic leaders, after they had studied the evidence, that they were convinced of the government's case. Subsequently, the archbishop accepted the resignations of the four priests who had been in charge of the infiltrated church organizations, suspended them from preaching and from having any contact with these organizations, closed down one of these organizations, and ordered all his priests not to mix religion and politics in their sermons. These actions, and the publicity given to them by the Vatican Radio, contradict Mr. Richburg's claim of a "split {in} Singapore's Catholic Church."

Mr. Richburg's omissions undermine his thesis that the Singapore government's actions "are part of a concerted effort to stamp out all forms of opposition to the ruling People's Action Party."

Subversion threats are not new to Singapore. For three decades since the 1940s, the Communists infiltrated legitimate organizations such as trade unions and Chinese middle schools. They mounted strikes, demonstrations and riots, causing chaos and bloodshed, in order to violently overthrow the legally constituted government.

The British government of colonial Singapore found it impossible to secure convictions against such communist agitators in court under the normal rules of evidence in criminal trials. Witnesses were afraid to testify for fear of being assassinated. The colonial government had to enact a law empowering it to detain, without trial, persons acting in any manner prejudicial to the security of the country.

This law has remained in the statute book because the problems have remained. The constitution of Singapore, the supreme law of the land, expressly provides for preventive detention. In six successive general elections, in 1963, 1968, 1972, 1976, 1980 and 1984, the communists, their fellow travellers and some opposition parties have campaigned against the Internal Security Act. Each time the electorate has given the government their overwhelming mandate.

The Singapore government is accountable to the people of Singapore. At the upcoming elections the people will decide whether this action was to forestall public disorders, violence and turmoil or whether they should support the opposition, which claims that it was to stifle dissent.

TOMMY T. B. KOH Ambassador, Singapore Embassy Washington