For some time now, Attorney Gen. eral Griffin B. Bell has been saying that he "had reason to believe" that accused South Korean agent Tongsun Park wanted to come back to the United States.

Now it is apparent why. Last September, less than a month after Park was indicted on bribery charges for his alleged role in a Korean government sponsored lobbying campaign, Bell had talked to Park on the telephone from Seoul. The conversation took place after Bell had been summoned to the Watergate South apartment of Tandy Dickinson, right down the hall from Bell. Dickinson is a close personal friend of Park.

Yesterday, in a telephone interview, Bell described the unique approach by the fugitive Korean businessman to the nation's top law enforcement officer. Sunday's New York Times carried an account of the contact, based on a memo Bell had written the day after it took place.

"A woman [not Dickinson] knocked on the door and said Tongsun Park wanted to talk to me, that he was on the phone," Bell said. "I said you must be kidding. I had a split second to decide if I was being set up. But I thought maybe he wanted to surrender, so I figured, what the hell, I'll go."

Bell said that when he got to Dickinson's apartment, she was talking to Park on the phone and handed it to him. "I'm satisfied that the man I was talking to was Park," the attorney General said. "He said he heard that I was a fair man, and said, 'I love the United States and I'd like to get my troubles worked out.'"

Park then asked Bell to discuss his case with Bobby Lee Cook, a prominent Georgia lawyer, the Attorney General said yesterday. "But I told him he already had a lawyer and that it wouldn't be proper unless Mr. (William G.) Hundley was involved.

"I didn't want to say much because I shouldn't be talking to a client without his lawyer," Bell said. "That call put me in a bad position, but I would have been an idiot if I hadn't taken it because he was a fugitive, he might have wanted to surrender."

Bell said the call from Park "fit in" with a call he'd received about a week earlier from Rep. John J. Flynt Jr. (D.-Ga.), who also mentioned that Cook was representing Park. Flynt is chairman of the House Committee on Standards of Official Conduct, which is conducting a parallel investigation of misconduct by members. Bell said he also talked with Cook later.

That contact did not lead directly to the arrangement the Justice Department made with the Korean government, which led to the current questioning of Park in Seoul. But it apparently was the first indication that Park intended to return.

Park, a wealthy Washington rice dealer who was known for the lavish parties he gave, left Washington for London in the fall of 1976 after coming under increased scrutiny by federal investigators for his part in the Korean lobbying effort. He left London for Seoul last August, just days before a federal grand jury in Washington handed down a 36-count felony indictment against him.

American reporters in Seoul have reported that during the current questioning Park has described payments of more than $750,000 to different members of Congress between 1970 and 1975.

Cook, the Georgia attorney involved in last September's approaches by Park, said in a telephone interview from his Summerville, Ga., home yesterday that Park first contacted him by telephone from Seoul in mid-September, asking him "to make some preliminary inquiries."

He declined to describe the conversation, but said that he had not known Park before and hasn't met him since.

He said that he never really officially represented Park during that period, and that "as far as I am concerned, nothing ever came of it."