Rhodesia's leaders flew to Pretoria yesterday to meet South African Prime Minister Pieter Botha as their administration faced crisis over possible postponement of the transition to black majority rule.

At the same time, two key black nationalist parties in the government held secret strategy talks prior to an important conference today prospects for meeting the Dec. 31 deadline for majority rule.

A government spokesman said Prime Minister Ian Smith and his three black colleagues in the interim government - Bishop Abel Muzorewa, the Rev. Ndabaningi Sithole and Chief Jeremiah Chirau - had gone to South Africa but he declined to eleaborate on the purpose of the trip.

Official sources in Pretoria said the Rhodesian leaders had met Botha but they declined to disclose details. It was the Rhodesians' first meeting with Botha since he succeeded John Vorster as prime minister Sept. 28.

In Salisbury, top executives of Muzorewa's United African National Council and Sithole's Zimbabwe African National Union discussed possible consequences of a failure to achieve majority rule by the target date.

Smith and Chirau have said that delay beyond Dec. 31 is unavoidable because more work is needed on a constitution. But Muzorewa and Sithole have declared that the deadline must be met. Spokesmen said after yesterday's meeting that their position had not changed.

David Mukome, spokesman for Muzorewa, showed optimism that the target date could be met. "We believe Ian Smith has just about run out of tricks," he said. "A bit of pressure can make him toe the line."

The entire transitional government - the Executive Council comprising Smith and the three nationalist leaders, and the second-level ministerial council made up of nine blacks and nine whites - is to discuss the issue today.

Military headquarters meanwhile, announced that 33 people had been killed in the guerrilla war in 24 hours. They consisted of an Australian captain in the security forces, 23 guerrillas and three collaborators, and one white and five black civilians.

Almost 5,000 people have been killed in Rhodesia this year, according to official statistics.

In Bulawayo, a spokesman said police have arrested 266 young blacks who staged a peaceful demonstration against conscription.

The demonstrators - many of them students - marched down Bulawayo's main street Tuesday carrying placards protesting against national service for Africans, and were taken away in four police trucks.