South Korean President Chun Doo Hwan today promised to hold national elections next year but indicated that many politicians active in the past will not be allowed to participate.

In an inaugural address this morning, Chun said that South Korea is due for "a change of generations among politicians" to eliminate what he called "the political extremism" of the past.

The former general, who recently stepped out of uniform to take over the presidency, did not spell out concretely his plan for restricting the elections but it appeared he was ruling out previous political leaders active both in the opposition party and the party that supported the late president Park Chung Hee.

He denounced the recent political past as tainted with "agitation, irrationality, factionalism, intrigue, irregularities and corruption."

It is my belief that we cannot risk putting the helm of state in the hands of such politicians," he said. "I am convinced, therefore, that the renovation of our political circles and a change of generations among politicians are unavoidable."

That description appears to exclude all three prominent political leaders active until Chun's troops seized total control of the country May 17 They are Kim Dae Jung, the principle opposition leader who is on trial for plotting renounced politics after weeks of house arrest; and Kim Jong Pil, the one-time progovernment party leader who was arrested on corruption charges and forced to surrender his personal fortune.

Several other politicians have been arrested and apparently will also be prohibited from the next campaign.

The inaugural address was Chun's first detailed prescription for South Korea's political future since he began his rise to power by seizing control of the military and pushing aside a weak civilian government. The United States, which bases nearly 40,000 troops here under a security agreement, has called on Chun to hold elections that would lead to a broadly based government.

Besides restricting the candidates, Chun also said he intends to hold the election with some kind of limitations on campaigning. He said they would be conducted with "free and fair competition" but with "unproductive, overheated campaigning forestalled."

Chun said the elections would be held under a new constitution in the first six months of 1981, but hinted that the schedule would be moved up if a "cooperative atmosphere matures satisfactorily." The new constitution is to be drafted quickly and submitted to a national referendum in October, he announced.

Sources have said the new constitution will provide for the indirect election of a president by an electoral body consisting of more than 5,000 members elected in precincts. Before the military crackdown in May, both major parties had intended to draft a constitution calling for the direct election of the president.

Chun is serving as interim president under martial law and he is widely believed to be preparing to seek a full term probably lasting for seven years. He promised today to establish "a tradition of peaceful transfer of power" but did not explain when that would take place.

He also said martial law will be lifted when South Korea's political scene is stabilized, but it was not clear whether he intends to lift the military rule before the elections.

Chun said South Koreans should move toward democracy but only in a manner suited to Korea's history.

"Democracy is now regarded as a universal good," he said. "However, it is not indigenous to Korea, but was introduced only after the liberation from Japan (in 1945). Therefore, despite this nation's various efforts to practice democratic politics, we have repeatedly paid the price of trial and error in the absence of a foundation on which democracy could materialize."