Following broad hints from U.S. officials, the main South Korean opposition party is preparing to return to the National Assembly for the first time since its members resigned two weeks ago.

New Democratic Party leaders also have agreed to meet with prominent figures from the government party, left leaderless by the assassination of president Park Chung Hee, to discuss how they might cooperate in the legislature.

Both moves are the first signs since Park's assassination that the assembly possibly might be revived as a political institution if martial law is lifted and the interim government of Acting President Choikyu Hah is replaced by elected civilians.

The resignation of the opposition, which followed the ouster of opposition leader Kim Young Sam from the National Assembly, touched off wide-spread civil disturbances in several provincial cities. A dispute on how to deal with unrest reportedly helped spark the assassination plot, allegedly led by Korean Central Intelligence Agency chief Kim Jae Kyu.

South Korean sources here say the U.S. Embassy is encouraging the return of the opposition legislators, which is seen as the first overt expression of American influence in the question of what kind of new government is established.

U.S. officials have remained silent on that question ever since Park's killing last Friday opened the door for broad change. They have said that the U.S. interest is in achieving a more "broadly based" political arrangement than that which existed under Park's one-man rule.

What that means has not been defined, although hints have been dropped that the United States looks to changes within the National Assembly as the most likely forum for a broader based political system. There have been no indications whether United States officials are pressing for a more dramatic change, such as major amendments to the constitution that had given Park virually total power over politics.

Under Park's rule for trhe last seven years, the unicameral National Assembly had been little more than a rubber-stamp machine for his policies. Besides the progovernment Democratic Republican Party, of which he was president, Park could also count on the support of about another one-third of the legislature's members whom he personally appointed.

The New Democratic Party, although it actually outpolled Park's party in popular votes last December, remained a weak but vocal minority group without any real power.

On Oct. 4, progovernment assembly members expelled Kim Young Sam for his strident criticism of Park. Nine days later, all 66 legislators in his party resigned in protest, including many who had been rather sympathetic to the president.

Since Park's assassination, all open political discussion has been stilled for a period of mourning that ends Saturday with Park's state funeral and politicians from both parties have declined to discuss their strategies.

Sources said today, however, that the opposition's return to the legislature when it convenes Monday already has been discussed and will be approved over the weekend.

They also said that a meeting has been arranged between a few leaders of both opposition and government parties.

It will probably take place as soon as possible after Park's funeral. No agenda was set, but they are expected to talk about ways of making the assembly a working institution if democratic government is restored.

The major divisive point between the two parties is the question of whether the next president should be elected under Park's consititution. It provides for an indirect election by a National Council for Unification that overwhelmingly reflects the Park government.

The opposition's expelled leader Kim had demanded that this be replaced with a direct election. He is expected to renew his insistence once the ban on politics is lifted. It is doubtful that the government party will acquesce.

Meanwhile, the South Korean dissident community, under constant surveillance during Park's rule, has taken a wait-and-see attitude toward the present interim government.

Sources in that community said that had hopes of a "more democratic constitution" emerging from the present situation, but they declined to discuss any details of their current activities.

The forces that had opposed Park received what appeared to be an olive branch today from the interim government. Former president Yun Po Sun, who was placed under house arrest for his anti-Park statements, was invited today to be a member of the advisory committee planning Park's funeral.

Kim Young Sam, the ousted opposition leader, also was invited. The invitations are a purely honorary matter, but to some sources they seemed to indicate a willingness by the interim government to extend an offer of cooperation.

The key government leaders met again today without announcing what they were discussing. They include Gen. Ghung Sung Wha, the Army chief of staff who has become martial law commander; two other military leaders; five cabinet ministers and Prime Minister Choi, who automatically became acting president under the constitution.

Informed sources said that Kim Jae Kyu's plot to assassinate Park included plans for a possible raid by 60 to 70 heavily armed KCIA agents on an emergency cabinet meeting after the killing, the Associated Press reported.

The sources said the raiding party was in place last Friday when Kim killed Park and the president's chief bodygaurd, Cha Ji Chul, and a five-man KCIA squad killed other Park bodyguards.

Kim apparently wanted to have martial law declared and be in a position to manipulate the martial law commander, the sources said.