Attorney General Griffin B. Bell fearful that he might lose the chief witness in his biggest criminal case to date has ordered the Justice Department's Criminal Division to step up its efforts to bring Korean businessman Tongsun Park back to the United States.

Bell's order was prompted by political pressure from critics of the department's Korean investigation and by his personal fear that Park may soon flee his present residence in London for a country where he would be safe from extradition.

But the effort to bring back Park, who was allegedly the central operative in South Korea's influence-buying effort in Congress, is fraught with questions of procedure, politics, and prosecutorial ethics.

Park left Washington last fall when the criminal investigation of the Korean affair was still young. He told the Justice Department he would be gone for two weeks on business, and the department did not try to stop him. Park has since refused to cooperate with any of the investigations of the Korean case.

The Washington star reported yesterday that the House Committee on Standards of [WORD ILLEGIBLE] Conduct, which is pursuing its [WORD ILLEGIBLE] Investigation sent staff member [WORD ILLEGIBLE] London last week-end to [WORD ILLEGIBLE] Park.

The committee, in a statement prepared by special counsel Leon Jaworski with the approval of Chairman John J. Flynt Jr. (D-Ga), said that report was wrong.

Justice Department investigators, who have interviewed hundreds of witnesses and reviewed stacks of documents in the United States initially placed a relatively low priority on geting Park back from London.

For that, the department has been roundly criticized House members from both parties.

Bell ordered more intensive work on the issue after meeting last Friday with two House members. New York Democrats Elizabeth Holtzman and Jerome A. Ambro who told him that the failure to bring Park back raised serious doubts about the quality of the Justice Department investigation.

At that meeting: Bell said that he, too was concerned because of a haunting fear that Park might "become another Vesco."

The reference was to industrialist Robert Vesco, who escaped prosecution on bribery charges by fleeing to Costa Rica. That nation generally will not extradite criminal defendants to the United States for trial.

As long as he stays in England, Park would be within reach of American legal process. Under English law and treaties, Park could be questioned under oath in London extradited to the United States, or deported.

Most investigators on the Korean case agree that extradition would be the surest way to get Park back. But that alternative poses a ticklish ethical problem.

Park could be extradited if he were indicted for a crime set forth in the Anglo-American extradition treaty. Investigators say they now have sufficient evidence to convince a grand jury to indict Park on an extraditable charge. But Justice Department officials have said that, even if Park could be indicted, they lack enough evidence to convict him.

As a practical matter, that is hardly a problem. Almost everyone involved agrees that Park, by turning "state's evidence," could gain immunity from prosecution.

Ethically, however, it would be an abuse of the grand jury system to indict a defendant who could not be convicted. Accordingly, lawyers at Justice, anxious as they are to place some legal hold on Park, are saying that it would be unethical to indict solely to extradite.

Yesterday, Rep. Bruce F. Caputo (R-N.Y.), who has been pushing for months for faster action on the Korean probe, wrote Bell complaining about the failure to bring an indictment.

Caputo's letter said that Philip Lacovara, who was briefly chief investigator for the House-s Korea probe, agrees that "Mr. Park can be indicted."

Rep. Ambro and Holtzman have been pushing Bell to try other means of acquiring Park's testimony: letters rogatory (the international form of deposition) or deportation.

In a letter of Holtzman, Benjamin Civiletti, chief of Justice's Criminal Division, said that neither approach would be useful. He said that questioning by letters rogatory must be in writing, and that oral interrogation would be necessary to get information from Park. Deportation would be useless, Civiletti said, because it would only force Park to leave England for another foreign country.

In his conversations with members of Congress, Bell has placed great emphasis on the prospects of diplomatic arrangements that might bring Park back to the United States.

Bell has said that White House officials are dealing with the government of South Korea in an effort to force Park to leave his London haven. There has been no report on the progress of that effort.

Others involved in the investigation are talking about a more personal diplomacy, in which American officials would offer Park immunity and personal protection if he were to cooperate with the inquiry.

This could be enticing to Park if, as has been reported, he is fearful that the South Korean government may try to kidnap or kill him to prevent his testifying.