Capitol Hill ethics committees and federal prosecutors believe the Korean government earmarked millions of dollars to influence U.S. congressmen, but not many legislators are admitting they received the money. Now a principal figure in the scandal called Koreagate thinks she knows what happened to that money: Korean intelligence agents lost it at Las Vegas gambling tables.

That's the conclusion reached by Suzi Park Thomson, former aide to ex-House Speaker Carl Albert and, according to American intelligence sources, a KCIA contact. Her explanation is a conventient one for all parties concerned: money lost gambling can't be traced, and it lets congressmen who have vowed they never received money, despite lists that claim otherwise, off the hook.

Thomson makes her claim in a paperback written under tight security and due out next month. She continues to deny any involvement with the intelligence agency of her native country, but - disillusioned by U.S. investigators - she says she did some sleuthing of her own. And in Suzi, subtitled The Korean Connection, Thomson contends the Korean influence-buying scheme was a snafu that enriched a few House members but mainly benefited greedy KCLA agents.

Since Koreagate began to unfold, Thomson has been a mystery woman. After office hours as a $15,000-a-year-aide and confidant to Carl Albert, she played hostess to numerous congressmen and Koreans at intimate dinner parties in her Southwest apartment. When her name began making front-page news. Thomson shunned the spotlight, speaking in halting, vague sentences when questioned by reporters. Eventually she testified before both a federal grand jury (taking notes which proved helpful writing the book) as well as the House ethics committee.

Last spring she signed a book contract with Condor Publishers and quietly began working with peripatetic author Robin Moore, who gained fame writing The French Connection and The Happy Hooker. Recently Moore has lent his name to a number of quick, thinly researched book projects, and in this case he will only approve the final draft. Working more closely with Thomson is Gene Zach, a former Hill aide and newspaperman.

"Somewhere along the way, Suzi got fed up with the way the grand jury and ethics committee were floundering," says Zach. (Investigators, on the other hand, say Thomson "stonewalled" during questioning.) "She developed an antipathy toward them because in the case of the grand jury she was treated almost as a criminal defendant. So she decided on her own to find out what the real story was, and she picked up this information from a variety of sources. The problem with these investigators was that they had a mind-set, they were dealing with self-fulfilling prophecies, and in their mind Suzi was part of the conspiracy."

Zach declined to be more specific about Thomson's sources for her Vegas gambling scenario, though he vows the book "is not any attempt to whitewash the government of Korea. The Korean government thought it was buying the U.S. Congress, but most of the money was sticking to the fingers of the Koreans handling the cash."

Other observations in the book:

For the first time, Thomson will detail her side of a 1973 affair with married congressman Robert Leggett. Two years ago Leggett denied receiving cash or favors from the Korean government, though while his affair with Thomson flourished, he made from the House floor statement of support for the Park regime in Korea.

Thomson will apparently play coy about any relationship with Carl Albert. "That's a murky area," says ghostwriter Zach. "There were some personal moments with Albert that can be read either benignly or otherwise. I've taken her as far as I can go on that, short of putting my hand on her throat . . . Where there are unresolved issues, I've left them unresolved."

Thomson will desribe a close friendship between Albert and his successor, House Speaker Tip O'Neill. Zach brands as inaccurate an earlier report that Thomson believes O'Neill received cash from Korean interests via poker games rigged in his favor.

Thomson will claim that KCIA agents "salted the mine," as Zach phrases it, by giving money to Otto Passman, Richard Hanna and Cornelius Gallagher, all ex-congressmen. That helped create an image of busy KCIA agents giving the Park regime its money's worth in Washington. Further, parties thrown by Tongsun Park, Korean Businessman and Washington lobbyist, featured political luminaries as guests, which also supposedly impressed the Seoul government. "Cash doesn't leave any footprints," notes Zach, who says the big money actually enriched the bagman's pockets.

Ex-Rep. Richard Hanna admitted accepting more than $200,000 from Tongsun Park and was sentenced last spring to 6 to 30 months in prison. Otto Passman, former Democratic congressman from Louisiana, was indicted on charges of accepting $213,000 from Park; he denies the charges. Ex-New Jersey Rep. Cornelius Gallagher, who once received an unsecured $250,000 loan from Park, was not indicted because of the federal statute of limitations, according to U.S. officials. The government agrees with Thomson on at least one of her points - prosecutors claim Korean-born cosmetic merchant Hancho Kim pocketed much of $600,000 he received from the KCIA to dispense to congressmen.

Says one reporter who covered the scandal: "H.R. Haldeman may have started a trend: you don't write your story , you tell your theory .Either she knew what was going on, or she didn't. If the latter is the case, she has stung a publisher."

Footnote: Suzi Thomson supports herself by working as a hostess at the Orchid Seven restaurant.