CAPE TOWN, South Africa — Ailing President Pieter W. Botha resigned Thursday as leader of South Africa's ruling white National Party, and Education Minister Frederik W. de Klerk, a more conservative politician, was swiftly elected to replace him.
Although Botha said he will retain the job of state president, the move appeared to signal the first step toward the end of Botha's 10-year rule, a decision hastened by a mild stroke the 73-year-old leader suffered two weeks ago. It also established De Klerk, 52, as Botha's most likely successor.
Some political analysts believe that the new party leader, though he has been a supporter of Botha's programs in the past, will slow down the step-by-step reform process begun under Botha and alienate more liberal party members.
"This is a definite setback for those within the National Party who argued for an enlightened reform process," Willie Kleynhans, a professor of political science at the University of South Africa, said in an interview Thursday night.
De Klerk, leader of the party in Transvaal province, declined Thursday to discuss his political agenda. He attempted to minimize his elevation, calling it "a party political affair with no direct or formal constitutional implications."
But analysts who closely follow National Party politics say De Klerk is the most likely replacement for Botha, perhaps when Botha's term expires in September.
Under South Africa's constitution, the majority party in the white chamber of Parliament--presently the National Party--has total control over the election of the president. The National Party is favored to retain its large majority in the next general election, which Botha must call within the next year. Before his illness, Botha expressed a desire to see his party through one more general election.
The battle over the presidential succession began two weeks ago when Botha suffered a stroke at his residence here. He lost some strength in his left arm and leg, but his doctors say he is recovering well. While Botha recuperates, his senior Cabinet minister, J. Chris Heunis, is acting state president.
For several months Botha has indicated that he wants to reduce the responsibilities of the president, perhaps by creating the position of prime minister to take care of ceremonial duties.
Botha's resignation after 10 years as party leader came in a letter delivered to a National Party caucus here on the eve of the opening of a new session of Parliament.
The president asked that the traditionally overlapping jobs of government and party leader be separated to reduce the workload. The 130-member caucus agreed and, on a third ballot, chose De Klerk over Finance Minister Barend du Plessis by a vote of 69 to 61, the state-run broadcasting company reported.
Botha has presided over the first important racial reforms undertaken by the National Party since it instituted the apartheid system in 1948. Essentially, these reforms have attempted to extend some political power to the black majority, without giving up white minority control, and to ease segregation, without eliminating it.
Johannesburg bureau assistant Michael Cadman contributed to this article.