Tongsun Park's lawyer said yesterday that the South Korean businessman is willing to return to London and face extradition proceedings on a secret criminal indictment filed last week by a federal grand jury in Washington.

William G. Hundley, who has represented Park during investigations of his role in South Korean influence buying in Congress, said that in a telephone conversation with his client in Seoul yesterday. "We agreed that if they [Justice Department officials] would tell us they think they have an extraditable case, he'd get on a plane for London and we'd be glad to litigate the matter," the attorney said.

A Justice Department spokesman declined comment last night on Hundley's remarks because the department has not officially acknowledged the existence of the sealed indictment.

The Washington Post reported yesterday that Park was indicted secretly last Friday in an apparent attempt to keep the criminal charge from being publicly known until Park returned to London.

While the exact charge is not known, it is believed to relate to the federal bribery statutes, which are extraditable.

Park has been living in England since he left the United States suddenly last fall during a Justice Department investigation of cash and gifts to members of Congress. He flew to Seoul last week, reportedly to visit his ill mother, and held a press conference in which he denied that any of his U.S. activities were illegal.

The United States has an extradition treaty with Britian, under which persons charged with serious crimes can be returned to stand trial. The proceeding can take several months, especially if the person fights back legally, as Hundley said Park plans to do.

Justice Department officials had expressed concern privately that news accounts of the secret indictment might cause Park to remain in South Korea indefinitely to avoid the possibility of extradition proceedings in London.

Hundley said yesterday that he had advised Park to stay in Seoul until Justice Department attorneys confirm the indictment. He said that he was considering filing a motion in court to have the indictment unsealed.

The attorney also said he was puzzled by the timing of the indictment because he told Justice Department lawyers last week that Park was planning to return to London early next week.

Rep. Bruce F. Caputo (R-N.Y.). a member of the House committee conducting a parallel investigation of members' ethical conduct, said yesterday that he also was troubled by the timing.

He said that evidence to indict Park had been available for seven months and that last Friday's grand jury action might be "a case of too little too late."

Caputo wondered why Park hadn't been indicted two week ago when he was in London and "could have been detained by U.S. authorities." He said the timing of the indictment "reminds me of a Peter Sellers movie."

While Justice Department officials continued to decline comment on details of the indictment or the strategy behind it, there were indications that it was timed to conincide with undentified "high-level diplomatic negotiations" with Seoul which Carter administration officials have alluded to recently.

"You'll just have to believe that we had our reasons, that we all aren't crazy down here," a Justice official involved with the case said.

Hundley said he will try to force Justice to make the indictment public and then file a motion to have the charge dismissed on grounds that the government used illegal intelligence intercepts to obtain some of its evidence against Park.

The Washington Post reported last fall that U.S. intelligence agencies had found that Park was part of a concerted lobbying effort on Capitol Hill which the South Korean government started in about 1970 to ensure continued U.S. aid.

Korean government officials and Park consistently have denied that Park was acting on behalf of President Park Chung Hee's Seoul regime. But The Post has reported that Tongsun Park had ties with the Korean Central Intelligence Agency dating back to the early 1960s.

There is evidence since the late 1960s that the Washington-based businessman was given Seoul government funds and an exclusive rice agent's contract.

If Park's criminal case reaches the extradition proceedings stage in London, Hundley said, U.S. prosecutors will have to present evidence and witnesses to back up the indictment.

Since that procedure could take several months, both sides agree, it would delay both expected criminal trials, where Park would be needed as a witness against former members of Congress, and the separate investigation by the House Committee Standards of Official Conduct.

Except for Caputo, committee members and staff attorneys declined comment yesterday on the Park indictment. It was learned that the Justice Department did not inform the committee of the sealed grand jury action.