In a significant indication that President Park Chung Hee may be moving toward relaxation of his authoritarian rule, South Korea's National Assembly voted unanimously today for lenient treatment of jailed political dissidents.

While urging Park to seek national harmony and the preservation of political and social stability, the legislature recommended cancellation of a 1975 emergency decree that bans most forms of political dissent. Such a step would clear the way for the release of up to 200 persons, including former presidential candidate Kim Dae Jung, jailed for violating the 1975 edict, known as Decree No. 9.

The legislature's recommendation is not binding but the president's control of the National Assembly is such that its move amounts to Park publicly sending a message to himself. The government-controlled South Korean press is interpreting the action as the precursor of a political relaxation.

Any easing of Park's rigid rule would be welcomed in Washington as consistent with President Carter's human rights policies If a thaw comes, however, it is more likely to be bound up in South Korea's internal dynamics than any wish to please an American president already pledged to remove 33,000 U.S. ground troops over the next four or five years.

Since Park, a former general, came to power in 1961 he has followed a policy of increasing repression interrupted by brief periods of liberalization. In the past, student riots and significant growth in opposition activities have prompted Park to call of his relaxation of controls.

The assembly's stage-managed advice that Park should lift the emergency decree was part of a three-resolution package dealing with the changing realitics of South Korea's situation. Referring to the planned U.S. troop withdrawl the lawmakers asked for gradual and cautious execution amid diplomatic and military safeguards.

The National Assembly "cordially" invited Washington to take action against what it called unfair anti-South Korean propaganda activity in the United States. Although unnamed, the apparent target of the complaint was the investigation ino allegations that the Seoul government bribed U.S. politicians and its responsibility for the kidnaping of Kim Dae Jung from Japan in 1973.

According to the National Assembly resolution. Park's opponents have exploited sympathetic figures in the U.S. press and Congress. The result, said the lawmakers, gave the impression that the United States was interfering in South Korean domestic policies.

There is no possibility that the appeal for a relaxation of political repression arose spontaneously in the National Assembly against Park's wishes. The revised constitution that Park forced through under martial law conditions in 1972 gave him virtually unlimited powers and placed severe restraints on the Assembly. One-third of its members are personally appointed by the president and the additional support of members from his Democratic Republican Party insures him overwhelming control of the Assembly.

Today's recommendation that even the jailed dissidents should be treated generously so they may join the cause of national development, is said to stem from a meeting in May between Park and opposition leader Lee Chul-Sung Lee. under attack within his own party for being overly pro-govrnment reportedly agreed with the president on the need for political development.

Newspapers in Seoul are speculating that the political prisoners may be release as early as South Korea's Independence Day, considering Dark's previous history of off-and-on controls it appears that a new phase in his duelling with a small but intransigent group of opponents is in the making.

Park's strongest rival for power, Kim Dae Jung, won 46 per cent of the vote and almost defeated him in the 1971 presidential election. Kim figured in a celebrated political trial last year and is currently serving a five-year prison term. With a group of other leading political and Christian activists. Kim issued a manifesto calling for Park's resignation.

They were accused under the May 1975 emergency decree put into effect after the fall of Indochina to the Communists. Park proclaimed the measure as necessary to eradicate splits in national unity at a time of heightened danger from North Korea. Under it any criticism of the constitution, political activities by students and any reporting of them in the media were deemed crimes detrimental to national unity and punishable by a minimum of one year in prison.

The hardcore opposition coalition of students, Christian activists and politicians have campaigned for repeal of the measure. Even strongly pro-Park elements in South Korea believe the government is sufficently powerful and popular that a measure of political activity is possible.

The outcome is still unpredictable. Kim Dae Jung and other opponents of park are unlikely to accept silence as the price of freedom. They have always insisted they can mobolize irresistible peaceful forces against Park's rule, and if given the opportunity, will undoubtedly again atempt to do so.