For 12 years, Richard T. Hanna, a bouncy, personable congressman, was so unexceptional that a Capitol Hill aide said of him yesterday, "I never identified him with legislation."

But for much of that period, Hanna was leading an extensive, hidden life that included outside business activities, fashionable parties, global travels and a web of embroilments with high South Korean officials and agents, according to the federal indictment of businessman Tongsun Park.

Hanna named as an unindicted co-conspirator, emerges as a key figure in the government's case against the Korean alleged to be at the center of his country's lobbying, bribery and influence-peddling here.

In page after page of details, the federal indictment portrays Hanna, 63, as an omnipresent middleman between the South Korean government and Congress for matters of business and foreign policy.

He was in business with Park, from whom he received more than $100,000, the federal charges say. And he shared with Park commissions from the sale of U.S. rice to South Korea while he was still repesenting his constituents in Orange County, California.

Until 1974, few of Hanna's colleagues knew him as anything more than what he seemed to be - a gregarioys, energetic politician with a goatee and a flair for doing vaudeville soft-shoe routines at parties where congressional people gathered.

But by then, by his own account, Hanna had come into his own as a special friend of South Korea in Congress. Since 1968, Hanna often was present in Seoul when the U.S. government financed large sales of surplus rice to the Asian country.

At the American embassy, Hanna began to be called the "California rice salesman," because he frequently showed up in Seoul when major rice transactions were in the offing. According to the indictment, more was involved than an interest in promoting the sale of the surpluses of rice produced year after year by California farmers. It states that it was part of the criminal conspiracy for Tongsun Park to "directly and indirectly give part of the commissions on the sale of rice to Richard T. Hanna and various other United States congressmen and senators . . ."

According to one source, the authoritarian president of South Korea, Park Chung Hee, took a personal liking to the jovial Hanna. "He was the only person - American or Korean - who I ever saw allowed to pound Park Chung Hee on the back and give him a bear hug," the source said.

In 1971, Hanna became a silent partner of Tongsun Park in an export-import venture that brought the congressman $60,000 to $70,000 over three years. Hanna never attemped to conceal his business connection. He reported it to the House of Committee on Standards of Official Conduct. But few of his colleagues noticed.

"We certainly didn't know he was in business with Park" said a California congressional aide yesterday.

In a long interview with The New York Times last year, Hanna said he had joined the business association to help Park out. He said he placed $90,000 worth of stock in the hands of the Equitable Trust Co. of Baltimore so Park could draw a $25,000 loan. Hanna said he later received money from Park and asked no questions.

In the years that followed 1971, Hanna said, he became uncomfortable with the business relationship, and eventually it was terminated. "There came a time when I recognized this was not so good," he was quoted as saying.

Nevertheless, for as long as he was in Congress, Hanna received VIP treatment in trips to Seoul, where a car and house were at his disposal, sources say.

At the endof 1974, Hanna ended a congressional career that began in 1963 by retiring to enter business. He worked for a California export-import business that traded agricultural comodities.

However, he continued to come to Washington, where he regularly stayed with Park, and kept some of his clothing in one of Park's homes. A file card box seized by the federal government last fall under subpoena belonged to Hanna. It contained the names key business and political contacts in Asia, the Middle East and the Soviet Union.

Several months ago, Hanna reportedly closed his offices in California, sold his house and moved in an attempt, according to friends, to remain incognito. He told former staff members that he feared he would be made a "scapegoat" in the Korean corruption investigation.