President Carter has sent at least one personal letter and several messages through American diplomats to South Korean President Park Chung Hee over the past three months asking for the return to the United States of Tongsun Park, administration sources said yesterday.

Carter's efforts and those of other senior U.S. officials have intensified since the Korean businessman went to Seoul from Lond Aug. 18 and a federal grand [LINE ILLEGIBLE] indictment against him Aug. 26 which charged that he was a secret agent of the South Korean government, informed officials said.

In the judgment of the Carter administration, they added, the Tonsun Park case now seriously threatens to impair U.S.-Korean relations. In this view, U.S. military as well as political relationships, including Carter's plan for the graudal and compensated [LINE ILLEGIBLE] troops, are not to risk.

In another indication of rising concern. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said that South Korean lack of cooperation in the Tonsun Park case can "only strain" U.S. relations with Seoul. O'neill said doubts about the continued advisability of aiding South Korea are being expressed throughout this country, and added that "the alliance cannot thrive" under these conditions.

O'Neill has been a strong supporter in the post of U.S. military and economic support of South Korea. In view of this and his powerful position, O'Neill's statement at the start of yesterday's House session was seen as highly significant. In recent days O'Neill has been embarrassed by what he charged is an "unfair story . . . a terrific smear" that Tongsun Park used O'Neill's office to receive messages.

Former Watergate Special Prosecutor Leon Jaworski, special counsel to the House Committee on Standards of Official Conduct, which is investigating charges of Korean influence-peddling, paid a 20-minute call on Secretary of State Cyrus R. Vance. Jaworski, who would not discuss the results of his meeting, has been asking for strong executive branch efforts to obtain the testimony of Tongsun Park and records relating to his activities.

In a rare official comment on the case, the South Korean embassy said in a statement yesterday "that the government of the Republic of Korea has never appointed Tongsun Park as an agent, and what he did or did not do was not done with the foreknowledge, approval or cooperation of the government of the Republic of Korea."

The statement said the Korean government "does not condone illegal acts on the part of any citizen," but did not say whether it would help return Park to the United States to face charges.

U.S. officials said there is no indication that the South Korean government has decided to make Tongsun Park available to American authorities or return him to Washington. In a conversation with two visiting members of Congress last Wednesday, South Korean President Park Chung Hee claimed that the "human rights" of the businessman-lobbyist are at stake.

Rep. Les Aspin (D-Wis.), one of the lawmakers present, quoted the Korean leader as saying that U.S. Ambassador Richard L. Sneider has been raising the issue of Tongsun Park's return "quite frequently" and that Sneider at one point asked, "Couldn't you just put him one a plane?"

"he [President Park] smiled and said to us, 'But we wouldn't want to violate his human rights, would we?'" Aspin said.

The meeting with the congressmen had begun with a 45-minute discussion of congressional concern about alleged human rights violations by the authoritarian park regime.

In Seould, Keyes Beech of The Chicago Daily News quoted a source close to the Korean president as angrily charging that the United States was demanding that South korea "violate its own sovereignty and constitution and in effect kidnap" Tongsun Park and "deliver him bound and gagged" to U.S. authorities.

The kidnaping technique was employed the other way in August, 1973, when President Park's most prominent political opponent, Kim Dae Jung, was bound and gagged by Seoul's secret police and kidnaped from Tokyo to Seoul. Kim is now in prison in South Korea despite repeated expressions of concern from Washington and Tokyo.

The South Korean president, who is not believed to be related to the Washington businessman, was quoted by Aspin as saying there was no truth to the allegations that Tongsun Park was connected with his regime. If any such connections were found he would take "drastic action," Aspin quoted the Korean leader as saying.

Aspin quoted President Park as saying that the report of a South Korean investigation of Tongsun park's activities has been turned over to the United States via Ambassador Sneider. The Korean president was also quoted as saying that he had tried to persuade Tongsun Park to return to the United States voluntarily but had failed.

The growing debate about the Korean government's cooperation is expected to come to a test vote in the House today on an amendment to the fiscal year 1978 budget resolution by Rep. Bruce F. Caputo (R-N.Y.). The amendment would cut the budget ceiling by $114 million, an amount equal to proposed U.S. aid to South Korea, as an expression of congressional displeasure.

Carter administration officials said executive branch concern about the South Korean position had increased sharply after Tongsun Park went home to Seoul and thus was subject to greater government control, and especially after he was permitted to hold a news conference in Seoul Aug. 24.

President Carter's personal intervention in the case goes back at least until June, officials said. They forecast more action by Carterin coming daysunless the Seoul government responds favorably.