South Korea's most prominent opposition leader, Kim Dae Jung, emerged from months of house arrest today and promptly indicated he expects to run for president under a new, liberalized constitution.

Freed from restrictions after nearly a year by a presidential order, Kim said he looks forward to being a candidate and feels his chances of being elected are good if his country gets a new "democratic consitution" and if a fair election is held.

"If we have those, I believe I have a good chance," he said in an interview at his home. "If not, it is hopeless."

The man who ran a close race against the last President Park Chung Hee in the country's last open direct presidential election in 1971 was free to move around and entertain visitors at midnight, after house arrest restrictions were lifted as part of the government's move to free political prisoners jailed under one of Park's proclamations.

He spent the day entertaining political guests, old friends, and newsmen interested in hearing the views of the man who was Park's most persistent critic.

Many visitors were turned away in that time and he was prohibited from leaving the grounds, which were under constant survellance. His wife and maids were followed by plainclothesmen when they went to market.

Kim was sentenced in 1976 to a five-year prison term for violating a decree that prohibited any criticism of the government. He had served 33 months of it when Park granted his release last December. But his movements were curtailed when he again began criticizing the government.

The new interim president, Choi Kyu Hah, announced on Friday that the proclamation would be abolished and 68 remaining prisoners freed. All those under investigation or restrictions for having violated the decree were also freed.

Choi this week was elected the successor to Park, who was assassinated on Oct. 26, but he has indicated he will serve only a limited term while the constitution is ammended and the way cleared for election of another president. Most observers think the election will not be held for at least a year.

Despite his optimistic comments, Kim readily agreed today that many obstacles stand in his way of becoming a candidate.

For one thing, he cannot legally run unless his civil rights are formally restored by presidential order.Choi has indicated he favors restoration of civil rights in general, but it is not known how he feels about reviving the political life of the man who got 45 percent of the vote in the 1971 campaign against Park.

Another hurdle is the almost certain opposition of the military, which has wielded great influence since martial law imposed was the day after Park was slain.

In the past few weeks, the martial law commander, Gen. Chung Seung Hwa, has let it be known quietly that the military does not want to see Kim become a candidate. In meetings with newspaper editors, he has charged that Kim was a collaborator with Communists before the Korean War broke out in 1950. That record precludes anyone from becoming president just as it would preclude a soldier with former Communist associations from becoming an officer, he is reported to have told the editors.

Kim, who said he was aware of the general's comments, denounced them as false. "That's totally untrue and there are many, many evidences to support my purity," he said.

Kim's first move after restrictions were lifted was to issue a political statement which, although moderate in tone, called for an early lifting of martial law, the release of all political prisoners, the restoration of their civil rights, and early amendment of the constitution.

He also called on Choi to appoint a "neutral cabinet" representative of the country's many interest and for establishment of a broadly based national consultative body to advise the president.

In the interview, he was more directly critical of Choi and more dubious about the possibility of creation of a democratic constitution and fair elections.

"I am skeptical . . . that we can follow a smooth process to amend the constitution and hold elections," he said."And so I am carefully watching Choi's attitude especially in forming a new cabinet."

The question, he said, is whether Choi constructs "another Park regime" or forms a broadly representative neutral government. The cabinet, he said, should include members of both political parties, dissident groups, journalists and prominent scholars.

Choi is expected to name a new cabinet and prime minister sometime next week.

Most of all, Kim said, he is concerned that so far Choi has not spelled out a timetable for his interim presidency, indicating how long he will serve and when the constitutional amendment process is to be finished and elections held.

The absence of such a firm schedule, he said, explains the concern of dissidents who recently staged two large protest meetings. They were brooken up by police and more than 100 persons were arrested for violating martial law.