South Korean President Choi Kyu Hah resigned today, opening the door to military strongman Gen. Chon Doo Hwan to take over as president of South Korea, perhaps by next Friday.

Speaking from the presidential Blue House on nationwide television, Choi announced that he was turning over the government immediately to Acting Prime Minister Park Chung Hoon. The constitution provides that the prime minister succeed the president in the event of a vacancy in the nation's highest office.

Park, in a statement issued four hours later, indicated that his term as acting president would be brief.

"A new national leader should be elected as expeditiously as possible," Park said.

South Korean political sources said that Park was expected on Monday to call the National Conference for Unification into special session next Friday to elect another interim president. The conference is a semi-electoral body set up by the late president, Park Chung Hee, in 1972 to rubber-stamp the selection of South Korea's president.

Indirectly, Park made it clear that the interim president would be Chon.

The only man other than the late president and the outgoing president named in his statement was Chon, whom he praised for his "resolute leadership" as chairman of a standing committee of a junta-like group that has been ruling the country since nationwide martial law was implemented May 17.

A background paper issued by the Ministry of Culture and Information also emphasized that Chon's leadership and the social reforms he has ordered had "established a basis to create a national consensus and a democratic welfare state."

The people have responded to Chon's leadership by "manifesting a popular will to open a new era," the paper said.

Choi in his speech, cited "my own political responsibilities for having caused great anxiety among the people" because of social disturbances last May.

"My purpose [in resigning] is to provide a historic turning point for the building of a new, happy community of stability, morality, and prosperity," Choi said. "I in tend to put an end to our unhappy political history by establishing the precedent of a peaceful transfer of power."

Choi's resignation brought the political game in South Korea to an end and confirmed Chon as the winner.

A scorecard of continuing purges has yet to be tallied. Details of a new form of authoritarianism that Chon was expected to bring to South Korea have not been announced. Furthermore, it is unclear how passively the South Korean people will accept Chon as interim president until a new constitution is approved and then as a full-fledged president under the nation's new charter.

Choi's announcement today, however, appeared to end what was supposed to have been a period of transition from the authoritarian rule of Park, who was assassinated last Oct. 26, to a democratic government chosen in free and open elections, by mid-1981 at the latest.

It also served as a climax to the meteoric rise to power by Chon, 47, a longtime protege of the slain former president.

Chon took over the nation's military in December, the Korean Central Intelligence Agency in April, and the country in May.

In each move, what has come to be called "purification" -- a sweeping purge of the corrupt and the inept -- was carried out with a vengeance.

Few doubt that Chon is sincere in attacking corruption and ineptness, and a U.S. military official said Chon had a spotless background. "There is no hand hold on him, ethically," the American said.

"Purification," however, also has become Chon's chief weapon in consolidating his political power.

More than 30 senior generals, most of them considered truly corrupt and inept, were ousted in a Dec. 12-13 mutiny led by Chon. More than 300 KCIA officials, many known to be corrupt, were ousted by Chon in April.

Student demonstrations in the streets of Seoul and other major cities May 13-15 gave Chon the pretext to carry out an obviously preplanned move to take over the country May 17. Since then, purification has gone far beyond the corrupt and the inept.

The May 17 implementation of total martial law -- supposedly to restore public order -- gave Chon the opportunity to wipe out, politically, all three men regarded as likely candidates for president.

Chon arrested Kim Dae Jung, the opposition New Democratic Party's candidate in the last free presidential election South Korea had in 1971. Last Thursday, Kim was brought before a court-martial to be tried on a charge of plotting rebellion, facing a possible death sentence.

Kim Young Sam was put under house arrest and forced to resign Wednesday as New Democratic Party president. A third leader, Kim Jong Pil, was arrested and charged with corruption. Kim Jong Pil was a follower of the late president Park and had chaired the ruling Democratic Republican Party.