U.S. and South Korean officials were reported near agreement last night on a plan to return accused South Korean agent Tongsun Park to the United States to testify on his alleged scheme to buy friends and influence in Congress.

"We are near agreement and we are hopeful that it will be nailed down by the end of the week," said a highly placed South Korean official in Seoul. The official, who did not want to be named, said an agreement could be announced soon.

Assistant Attorney General Benjamin R. Civiletti, who is handling the Justice Department's role in the negotiations with South Korea, said yesterday a final agreement is so near that his department has prepared a news release to announce it.

"I think we're very, very close to an agreement," Civiletti said. "There are bits and pieces in both agreements which are still unresolved."

But Park's attorney, William G. Hundley, cautioned that there could be a last-minute snag in the negotiations to grant immunity to park in exchange for his testimony.

The agreement being negotiated reportedly would provide for Park to be interrogated in Korea by U.S. prosecutors. If at a later date the prosecutors sought his return to the United States to testify at one or more criminal trials, Park would do this. If he were to return to the United States, Park would also be subpoenaed by one or more congressional committees conducting their own investigations of the scheme.

Park reportedly wants to avoid testifying before the congressional committees, and the dispute about this is one of the factors delaying the settlement.

Justice Department attorneys have privately expressed the hope that Park's testimony could lead to several additional indictments of past or present congressmen.

But the Korean government still refuses to acknowledge that Park had any official role in Washington, and it is unclear how Park could testify freely about the conspiracy he is alleged to have organized if his own government - which negotiated the arrangements for his testimony - denies that conspiracy took place.

Whether the Seoul government will now change its tune remains to be seen. It has come under intense pressure from Congress to make a clean breast of the influence-buying affair or face reductions in American aid.

A bill to transfer military equipment to South Korea was shelved in Congress this year because, its sponsors said, it was unlikely to pass in the acrimonious atmosphere created by the Park affair.

Though many details are missing, public accounts of the alleged Korean influence-buying scheme have described an elaborate system whereby Park and others used money from the South Korean government and from various business deals to make payments to congressmen.

In his 36-count indictment, Park was charged with conspiracy, mail fraud, bribery, racketeering and being a foreign agent. Another indictment in the case charged that Hancho C. Kim, a naturalized American citizen, had evaded income tax, lied to a grand jury and conspired to defraud the United States in connection with $600,000 he allegedly received from the Korean Central Intelligence Agency to pay and entertain U.S. officials.

Former Rep. Richard T. Hanna (D-Calif.) also was indicted on 40 counts involving bribery, conspiracy, mail fraud and failure to register as a foreign agent. The indictment charged that Hanna, at a 1967 meeting in Seoul with the director of the KCIA, helped hatch the original plot "corruptly to influence U.S. congressmen to take actions favorable to the Republic of Korea.