Tongsung Park's American lawyer arrived here tonight saying he will recommend that his client meet with U.S. investigators in a third country and give testimony on the congressional influence-buying scandal. He did not identify the country.

William G. Hundley, who practices law in Washington, confirmed reports in the South Korean news media that President Carter had offered Park immunity in exchange for his presence for testimony in Washington. The press here quoted South Korean government sources as saying that Park had rejected the offer.

Park, a once-prominent Washington social figure was indicted for conspiring to bribe congressmen in an effort to obtain continued American aid for South Korea.

He left Washington a year ago, when the news of an investigation of his activities was first published. He lived in London until late last month when he came to this country. He has said he will not return to Washington's "emotionally charged" atmosphere.

Neither Hundley nor the quoted Korean sources indicated precisely when the offer of immunity was made.

The U.S, embassy had no comment.

Hundley told reporters that the offer "would not apply to present times as far as I know."

The government sources were quoted as saying that the offer was made in Carter's letter to South Korean President Park Chung Hee, who passed it along to Tongsun Park.

Hundley was met at Seoul's Kimpo Airport by several of Park's business associates, who drove him away after two brief airport encounters with reporters. Park himself has been seen around town on several recent evenings, but did not show up to greet his attorney.

Hundley is believed to be urging Park to return to London.

Early this month, after initial news of the secret indictment had been published, Hundley said that Park would be willing to return to London and face extradition procceedings if they were brought by U.S. officials. The United States has an extradition agreement with Great Britain but not with South Korea.

Some observers here believe that the South Korean government would not be willing to let Park leave the country. However, its official position is that Park is a private citizen free to go where he chooses. Park is reported to be under government surveillance, although he has appeared to move freely about the country.

Hundley was asked if his trip here was timed for a possibly simultaneous visit by Leon Jaworski special counsel for the House Ethics Committe investigating the case. The committee has discussed sending Jaworski here to question Park if he refuses to go to Washington at any time.

Hundley said he knew nothing of Jaworski's plans and had not talked to him about a visit to South Korea.