Investigators for the House ethics committee get periodic phone calls these from the office of Rep. John J. McFall (D-Calif.). "We're just checking to see if we can be of any help," explains McFall aide Sam Mabry. "We'd like to get this thing over with."

McFall is among a number of congressmen whose relationships with South Korean businessman Tongsun Park are being closely scrutinized by the ethics committee. Both the committee and the Justice Department are investigating whether congressmen were improperly influenced by cash and gifts they received Park on behalf of the South Korean government.

McFall's case privides a good illustration of the problems that members of the ethics committee will face in trying to judge the conduct of other congressmen who became involved with Park.

McFall has acknowledged receiving large cash "contributions" from Park that he put into a secret office account. The California congressmen also has written letters to the President of South Korea on Tongsun Park's behalf.

McFall insisted in a recent interview with The Washington Post that he never thought Park was a South Korean agent. McFall said he is confident that he can show that he helped Park only because his constituents told him it would aid the California rice industry, which Park had represented.

McFall's problems began last fall, shortly after he was elected to an 11th term representing California's sprawling, largely agricultural 14th district, when he told a hometown reporter then that he had accepted cash from Tongsun Park.

At the time, the 59-year old McFall was majority whip, the third ranking member of the House Democratic leadership and a candidate to succeed Rep. Thomas p. (Tip) O'Neill as majority leader. But with the Tongsun Park's connection hanging over his head, he finished last in four-man race.

Then last month, The Post reported that McFall was among a group of congressmen who had written letters to South Korean President Park Chung Hee at Tongsun Park's request.

McFall refused to discuss the matter before that story was published. He since has made his file on the rice industry and Tongsun Park available to reporters and ethics committee investigators.

McFall recalls he first met Park in December 1969 apparently at a meeting requested by Curt Rocca in McFall's Rayburn Building office. Rocca is the owner of a rice storage facility in Stockton, Calif., and has a large financial stake in California rice.

At the meeting, Park apparently asked for an endorsement, McFall said, because a few weeks later, on Dec. 24, the congressmen wrote a glowing letter of praise of Park's help and assistance "in matters involving South Korea and the United States."

"I looked on him as a businessman who wanted some kind of to-whom-it-may-concern letter that he had done a good job, and we gave him one." McFall explained.

The letter was patterned after one written by Gov. Edwin W. Edwards of Louisiana, who then was a congressman. A copy of Edwards' Dec. 22 letter to Park is in McFall's file. "My surmise is that he (Park) might have brought it by as a sample of what other members had written thanking him for his good work," McFall said.

At the time, Park was a selling agent for the Rice Growers Association of California, a farmers's cooperation group located in McFall's district. McFall's file is filled with letters and requests from Robert Freeland, an RGA executive, and Rocca. McFall said he had the impression that Park was in business with both Rocca and Freeland. The congressman he said he did not hear from Park again directly for a year.

Then on Dec. 22, 1970, he wrote another letter to Tongsun Park, expressing satisfaction over a large sale of rice to South Korea.

McFall also noted in the letter that his membership on the House subcommittee handling foreign aid funding allowed him "to assist in advancing some of the presidential recommendations regarding aid for the country" (South Korea).

Hand-scrawled notes on that letter refer to "Korean politics" and the "U.S. State Dept." McFall aide who made the notations said he could not recall to what they referred.

Six months later, in June, 1971, Tongsun Park came calling again, according to McFall's office records. This time Park asked for a letter addressed to the president of South Korea, congratulating him on his re-election.

"He was obviously a supporter of President Park," McFall said. "I also thought of it in terms of this fella (President Park) is buying California rice and doing a good job of it. And if he's elected president he will keep on buying California rice."

In the June 18 letter, McFall expressed "confidence in his (Tongsun Park's) representations regarding Korea, especially in rice." McFall added that he hoped to expand friendships between the two countries "through good working relationships which we have already established through Mr. Tongsun Park."

McFall concluded this letter to President Park by saying, "Please let us know whenever there may be any problems for which you believe I may be of assistance in helping to achieve solutions."

A week later he was Tongsun Park's guest at a large dinner party at the George Town Club.

McFall said he did not hear from Tongsun Park again until shortly after the 1972 election. On Nov. 13, McFall's appointment book records that Tongsun Park and Steve Kim visited his office.

Steve Kim is the brother-in-law of one of Tongsun Park's top aides, B.Y. Lee, and has been identified as an agent of the Korean Central Intelligence Agency stationed in Mexico City.

McFall recalls that, while Steve Kim waited outside, Tongsun Park came into the congressman's private office and said, "Here's something to help with your campaign expenses." Park handed McFall an envelope containing $1,000 in $100 bills.

The congressman had no opposition in that election. "I recall saying, "Well, I don't have any campaign expenses. I'll put this in my office account. And we did, the very next day," McFall said.

On Feb 9, 1973, shortly after McFall was hand-picked by Tip O'Neill and then House Speaker Carl Albert to be the majority whip, Tongsun Park visited him again to arrange an April 16 George Town Club party in McFall's honor.

"I didn't want a party," McFall said. "But he was happy I was whip and wanted to congratulate me. When I saw the party I said, well I'm the excuse for a party.' There were a lot of people there . . . 100 or more."

The cohosts of the party were two Tongsun Park's closest congressional friends, Reps. Richard T. Hanna (D-Calif.) and William E. Minshall (R-Ohio).

On Feb. 23, a few weeks after the party planning session, McFall wrote a second letter to President Park, using a draft furnished by Tongsun Park. McFall said he asked for suggestions from Tonsun Park because he did not know what to say to President Park Chung Hee.

"Obviously I thought he was using these letters to keep his influence," McFall said. "He wanted to show the president that he was accepted in the U.S. for doing a good job selling rice and that this would keep whatever kind of 'in' he had for selling rice."

Despite the requests for these letters, McFall insists he never thought Tongsun Park was a South Korean government agent. He said he considered Park "a guy who was doing a pretty good job selling rice."

Though he attended another of Tongsun Park's large congratulatory parties - this one on Dec. 10, 1973, for O'Neill - McFall said he had no personal contact with Park for the next 18 months.

On Oct. 18, while McFall was campaigning in California a Park aide delivered another envelope full of $100 bills, this time to Ray Barnes, the congressman's administrative assistant at the time. This $3,000 "campaign contribution" again was put into McFall's private office account, rather than the candidate's campaign account.

When asked about this money last fall. McFall explained he put it in the office account because he thought the cash from a foreign national would have been illegal to accept as a campaign contribution.

Earlier this year McFall amended his income tax returns for 1972-75, reporting the contributions to his office accounts as income, and paying an additional $1,200 in U.S. tax. Besides buying office supplies, McFall used the money for interest free personal loans.

The McFall-Park relationship ended in late 1974, the congressman said. "It's hard for me even now to believe he was a lobbyist," the congressman said. "He didn't try to lobby me."

However, the ethics committee already has approved standards of judging conduct that could make McFall vulnerable to disciplinary action.

In a memorandum of legal procedures accepted by the committee last month. special counsel Philip A. Lacovara said that congressmen should be disciplined if the circumstances of a gift offer should have alerted him to hesitate and inquire before acting. "The failure to learn the truth should not be an excuse" in such a case Lacovara wrote.

This "affirmative duty of reasonable inquiry" should be imposed since all public officials should be conscious of the possibility that any substantial gift may be offered in an attempt to secure improper influence." Lacovara added.

McFall's peers will have to judge whether he made such "affirmative inquiry" before accepting cash from and doing favors for Tongsun Park.