House Majority Whip John Brademas (D-Ind.), a popular senior lawmaker whose 18-year congressional career has been free of taint, is finding it more and more difficult to escape the toils of the Korean influence buying scandal on Capitol Hill.

Brademas has spent a good deal of his time in recent weeks answering questions about a $2,950 cash contribution to his 1974 re-election campaign from Tongsun Park, the South Korean businessman who was indicted last month on charges of trying to bribe members of Congress.

The congressman has offered conflicting explanations of how he used Park's cash.

In an interview a month ago with The Washington Post, Brademas said all the cash had been spent directly for campaign activities.

Two weeks later, Brademas told his hometown paper, The South Bend Tribune, a different story. The congressman said then that $950 of Park's money ended up in his personal bank account.

If the South Bend version is accurate - and Brademas now says it is - it could propel the congressman into a complicated legal stew.

The House's Code of Official Conduct mandates that "A member . . . shall keep his campaign funds separate from his personal funds."

The Internal Revenue Code requires candidates to report as income any political contributions transferred to personal use. Brademas says he did not report Park's cash as income on his tax return.

The congressman says he was not required to report the $950 as income, because he took it to reimburse himself for an $800 campaign expenditure he had made with personal funds.

That explanation might entangle Brademas in another federal statute. Brademas did not report the $800 expenditure on his campaign finance reports. The Federal Election Campaign Act requires itemized reporting of any political expenditure over $100.

All these problems have made the earnest, cooperative Brademas angry and defensive about his relations with Tongsun park.

Brademas says the news 'reports of the cash contribution earned him the harshest editorial condemnation of his 18-year congressional career.' The papers savaged me," he says with an unhappy shake of the head.

The criticism is "just not warranted," Brademas says. "If I had wanted to pursue some nefarious purpose with [Park's] money, why would I have reported the contribution?"

Brademas' campaign committee publicly reported the receipt, on Sept. 23, 1974, of $2,950 from Tongsun Park. The reports also show a disbursement of $950 to candidate Brademas the next day.

The reports do not show how Brademas used that $950, however, and it is here that the Washington and South Bend versions of this story differed.

In his first interview with The Post, Brademas said he took the cash on a trip to California because he knew he would be entertaining a group of political backers there on Sept. 24 - the day after he received the money from Park.

In considerable detail, Brademas told The Post how he had folded the money - $950 bills - into his pocket in his office in Washington. Later that day in Los Angeles, he explained, he had counted out about $700 of the cash to pay the bill at a posh night spot where he hosted a dinner.

In the story he told The South Bend Tribune, however, Brademas said the Los Angeles dinner was actually held in May - four months before Park contribution.

Brademas told the Tribune (and The Post, in a subsequent interview) that he now cannot recall what he did with the $950 in cash. Somehow, however, it ended up in his personal checking account, the congressman said.

"It was all perfectly legitimate" to deposit the cash in his personal account. Brademas now says.

"By the time Park made this contribution, the $950 was really mine. I had personally paid $800 for that dinner in Los Angeles in May, and the campaign owed me for it. So when Park made the contribution, the cash was really my money."

At the dinner in Los Angeles in May, Brademas says, he entertained about 15 friends, including NBC newsman John Chancellor and two members of Brademas' committee staff.

Brademas said he would not ask for political contributions from the staff aides, and that he knew that Chancellor would not make a campaign contribution. But Brademas maintains, that the dinner was a political, not social function, because "there were some past and potential contributors there."

Those present at the Los Angeles dinner contributed a total of $400 to Brademas' campaign in 1974, according to campaign reports.

Brademas said he did not report the Los Angeles dinner as a political expenditure because "it just slipped my mind." He said he had never, before or since, forgotten to report a campaign expenditure of similar magnitude.

Brademas said he could not recall why he had wainted until September to seek reimbursement for the expenditure in May. "It didn't occur to me to reimburse myself until the cash contribution came in, I guess," he said.

The remaining $2,000 of Park's 1974 contribution was placed in Brademas' office safe and used for petty cash in the campaign, the congressman said.

Brademas for years sponsored legislation outlawing the use of cash in campaign contributions. He said he accepted the cash from Park, in violation of his personal rules, because the South Korean was "charming . . . it would have been awkward not to."