A former Methodist minister charged with high treason under South Africa's stringent security laws jumped bail and fled the country prior to the resumption of his trial yesterday.

Cedric Mayson, 55, was accused of being a member, or an active supporter, of the banned African National Congress, which is committed to trying to overthrow white-minority rule by force. The judge in the case sustained Mayson's charge that he was tortured during interrogation.

The onetime minister, who had assured friends and Judge Pieter Van der Walt that he wanted to face trial to prove his innocence, told a press conference in London today he decided to flee because friends and colleagues would have been endangered if the case had continued.

"They would deliberately have chosen to go to jail for contempt of court rather than give evidence against me, and the state knew this," Mayson said, according to wire services.

This was thought to refer particularly to C.F. Beyers Naude, banned former director of the proscribed Christian Institute. Mayson left the ministry to work with Naude at the institute. Naude, a well-known white Afrikaner dissident, had been subpoenaed to testify against Mayson but had told associates he would refuse.

The reports also quoted Mayson as saying he decided to flee because, even if he had been acquitted, he believed the security police would have detained him again without charges. He was held for 14 months without charges before being brought to court Feb. 7.

Mayson said a friend drove him near Lesotho Friday. He waded across the Caledon River into the little African state after wandering lost in the bush for nearly four hours. He flew from there to Mozambique, then to London, Mayson said.

When the Supreme Court assembled for the resumption of the case in Pretoria yesterday, Mayson's lawyer, Ernest Wentzel, handed the judge a letter of apology from the former minister.

Mayson's wife Penelope, who with their seven children seeks to join her husband in Britain, said bricks were thrown through windows of their house and car last night.

News of Mayson's flight surprised his friends, who said they had felt confident he would be acquitted. Although the treason charge was ostensibly serious, they said the low bail set by the judge indicated he viewed it as treason only in a technical sense. Bail is not usually granted in treason cases.

Mayson was detained by the security police Nov. 27, 1981, the same day as Neil Aggett, a young labor unionist whose subsequent death in detention caused an international outcry.