South Korean President Park Chung Hee, formally reelected to a six-year term, claimed yesterday that his tenure had brought the country from chaos to stability and prospertiy.

In a dry, unemotional speech, the president attributed the successes to the "grand reforms of national salvation," a reference to the radical political changes he fostered under martial law which he was elected in 1972.

"We have succeeded in building a solid foundation for national security by accomplishing outstanding growth, on the basis of stability in all fields of politics, economy, society and culture," Park declared to an admiring audience of supporters. "Now we are full of confidence."

He addressed the national conference for unification, a presidential electoral body which, as expected, proceeded to renew his tenure without opposition.

Gathered in a brightly decorated gymnasium in a downtown Seoul. 2.577 conference delegates voted for him in a secret ballot. One ballot was declared invalid on a technically and five delegates did not attend.

They had been chosn in May in an uncontested national election that was boycotted by the minor parties which sometimes oppose Park's rule because the law does not permit politicians to take part in presidential elections.

Park by law is chairman of the national conference which also will rubbert stamp his choice of one-third of the members of the National Assembly, the country's unicameral legislature.

As he embarks on a second term under the restrictive rules he laid down in October 1972. Park presides securely over a nation that is militarily stronger and vastly more prosperous than it was six years ago.

But it is also a country still wracked by internal dissent and occasional outbursts of bitterness over the suppression of civil rights. His last real political opponent, Kim Dae Jung, is still imprisoned, guarded now in a hospital room where his reading matter is restricted to non-political books and where visists by his wife are carefully watched by police.

The systematic torture of dissidents which marked the early 1970s has been abandoned and Park's government shows greater tolerance of public criticism. But sizable demonstrations of students are still broken up, sometimes violently, and many writers, including the prominent poet Kim Chi Ha, remain in jail.

Many observers here believe that the greatest danger facing Park is no longer the revolt of political dissidents but the rising impatience of workers in South Korea's booming factories.

Unorganized until recently and ignored by the government-guided labor unions, employes of several industrial plants have begun informal strikes, demanding higher wages and easier working conditions. Strikes are outlawed in South Korea.

In a series of protests, they have contended they are left behind in the country's new prosperity - abandoned workers whose low wages form the underpinning for South Korea's export economy. They assert that the government is guilty of backing up the factory owners to suppress labor activism.

The country is also beset by high inflation brought about by the high-growth policies of the last 10 years. The New Democratic Party, which offers a week opposition to Park's party, has taken up the inflation issue for the parliamentary election, contending that what South Korea needs now is stability, not rapid growth.

The president's speech was all sunshine and optimism, contrasting today's security and prospertiy with what he described as turmoil six years ago.

Now, he said, stability has been restored amid prosperity. That prosperity has created "an enormous gap in national strength" between South Korea and the Communist North, he said. "This new situation should have the effect of hastening the unification of the nation," he added.