Secretary of State Cyrus Vance will urge South Korean leaders to move in the direction of political reform but will not suggest that they make sharp changes immediately, U.S. officials said last night.

Instead, they said, Vance's feeling is that South Korea may move gradually toward change under the "existing structure" and that there is hope for more dramatic change "in the long range."

Vance has come to a city that is anxious to learn how he would try to use American influence in shaping the post-Park political climate. With the funeral now over, the moratium on political discussion that has been observed during the mourning period is ended.

Park was buried today following a solemn state funeral attended by missions from 40 foreign countries. About 2 million Koreans lined the streets of downtown Seoul as the funeral cortege moved slowly through the city to the National Cemetery. He was buried beside the grave of his wife, who was assassinated during a public ceremony in August 1974.

Family services had been held at the Blue House, the presidential mansion.

Then a van bearing Park's coffin was drawn down an avenue by military cadets to a plaza near South Korea's former capital building for the formal services.

Park's own voice rang out over the plaza as a tape recording of one of his speeches was played. The speech called for preservation of traditional Korean culture and national unity.

Acting President Choi Kyu Huh, one of Park's longtime confidants, eulogized the slain president as one who had preserved the country's security in the face of threats from communist North Korea and who had directed its rapid economic advances in the past decade.

Vance and President Carter's son, Chip, headed the American delegation that included several U.S. congressmen, Sen. S. I. Hawyakawa (R-Calif.) and the former U.S. ambassador to South Korea, Richard Sneider.

Some opponents of the late president were hoping for heavy American pressure to push the interim government toward an immediate amendment of the constitution, a move that would give opposition forces a stronger voice in choosing Park's successor.

Under the so-called Yushin Constitution imposed by Park, the successor would be chosen within three months by the same National Council of Unification that last year elected Park to a six-year term. It is likely to select someone with views similar to those of Park, observers here feel.

Before Park's death a week ago, leaders of the opposition New Democratic Party had pressed for a change that would let voters directly elect the president.

There has been no indication as yet from the military-dominated interim government what it has in mind and no guarantee that martial law will be lifted anytime soon. Yet the working assumption has been that martial law will be lifted in time for a new election within the prescribed three months.

Many politicians both in and out of influence under Park's rule said this week they looked to Americans for guidance on amending the constitution but they were far from agreement on what kind of guidance they hoped for and expected.

Vance's arrival has been expected to provide a key to understanding which way that influence would be directed.

U.S. officials said last night that in talks with civilian leaders here Vance will make "several comments" along the lines that he trusts the South Koreans will move in the direction of reform. But he will not urge any fast tinkering with the yushin Constitution and he will not suggest that the interim government lift the emergency decrees under which Park's government has jailed hundreds of dissidents in the past few years, they said. Those decrees, among other things, prohibit anyone from criticizing the government except within the halls of the National Assembly.

There is reason to believe, the officials said, that once the immediate succession question is settled the Korean leaders will move promptly toward "long-range change."

The State Department had been divided on the issue, with the embassy here and most East Asian affairs officials in Washington opposing pressure for sudden changes and the Human Rights bureau of the department favoring a specific declaration for reforms.

There has been speculation that a compromise might be worked out here that would fall somewhere between an immediate consititutional change and an undefinite perpetuation of the yushin system, which means "revitalizing reforms."

The officials said last night, however, that there is no agreement yet on what that compromise might be.

Vance arrived with a delegation of congressmen for Park's funeral. At the airport, he paid tribute to Park as a man whose leadership "brought Korea, in a remarkably short space of time into the ranks of economically strong and developed nations. His place in history is assured."

Meanwhile, supporters of the late President began a quiet campaign urging continuation of the present constitution for at least one year, contending that the need for continued stability overrides demands for immediate political reform.

Members of the Democratic Republican Party, which Park headed, began circulating that theory yesterday and are prepared to state it more vocally once the president is buried and the moratorium on political discussion, imposed for the period of mourning, is over.

It was not clear whether their campaign represented the thinking of the interim government, although it was noted that members of the ruling party met yesterday for the first time since Park's murder with Choi Kyu Hah, the acting president who meets daily with cabinet members and military leaders.

Vance was scheduled to meet today following the funeral services with Acting President Choi Kyu Hah.Last night he conferred with Foreign Minister Park Tong Jin.

Vance is not expected to issue a public statement but will make his position known in private conversations with those two leaders.

He was not formally scheduled to meet with Gen. Chung Sung Wha, the army chief of staff who became martial law commander last week and who is regarded as the most powerful figure in the interim government. But Vance may confer with Chung at a reception, officials said.