LOS ANGELES (AP) _ A businessman who gave $400,000 to the Republican Party is a political mystery in California, with an office he hasn't visited in six months and no apparent ties to local Republicans.

Michael Kojima, identified in state records as the president of International Business Marketing Ltd., was among the contributors invited to Tuesday night's President's Dinner, the GOP's premier fund-raising tool.

Kojima made two $200,000 contributions to the Republican Party, one on March 6 and the other March 18, according to Federal Election Commission records.

President Bush presided over the biggest political fund-raiser in history, a glittering Washington dinner that brought in $9 million as contributors paid top dollar to rub elbows with the administration's elite.

The minimum contribution for the President's Dinner was $1,500 per person. Kojima was foremost among the contributors, and sat at the head table along with the president and Barbara Bush.

The receipts included large amounts from corporate sources prohibited by law from contributing directly to candidates. They may legally give money to the political parties as long as the money does not go directly to federal campaigns.

Such corporate contributions are known as soft money.

Also in that category are large contributions to the parties from individuals, who are permitted by law to give no more than $1,000 directly to a candidate.

Bush today defended the GOP dinner and current rules on political fund- raising, saying the event was ''a huge success and everything complied with the law. So, don't buy into that old theory by the liberals that are trying to ram through government financing on everything.''

Rich Galen, spokesman for the President's Dinner, said that Kojima described himself as ''an investor in international consortia for large projects around the world'' such as airports.

Galen said he decided to question Kojima after reporters raised questions. He said Kojima was a ''newcomer'' at this level in the contribution process. He didn't get too detailed ''because you don't cross-examine a guy'' who is potentially a huge fund-raiser.

Galen said Kojima was a U.S. citizen.

In California, interviews with more than a dozen Republican and Democratic insiders failed to produce a single person who has ever heard of him. A computer search of local newspaper stories from the last two years also failed to produce Kojima's name.

International Business Marketing is listed by the state Secretary of State's office as a Wilshire Boulevard business consulting firm incorporated on June 27, 1990.

Secretary Lil Vasquez answered the phone at the Wilshire Boulevard office and said that Kojima rents an office from her law firm, Cummings and Pantaleo, but he is never there.

Vasquez said she didn't know Kojima's business. He has no employees working in the office and he used to call in for messages, she said.

''We haven't heard from him in six months. We thought he was out of the country,'' said Ms. Vasquez.

The Los Angeles County Registrar of Voters gives Kojima's voter registration address as being on Montana Avenue in the tony Brentwood section of Los Angeles.

But a woman answering the phone at that address, who identified herself only as Katie, said the address was not Kojima's home, but the office of a business run by Kojima's wife.

The business is Academic Recruit Corp., or ARC, which places Japanese students at all levels in schools around the United States, said Katie.

There is no listing in the California Secretary of State's office for a company by that name. Companies that are incorporated or limited partnerships must be registered with the state.

Among the political insiders who drew a blank on Kojima were state GOP spokeswoman Lorelei Kinder; Dan Schnur, a former state GOP spokesman and now a spokesman for Gov. Pete Wilson; big Los Angeles political contributor Richard Riordon; aides to Democratic politicians Rep. Mel Levine and Assemblyman Tom Hayden; and two top officials with the Bill Clinton presidential campaign, national Chairman Mickey Kantor and California campaign manager Geoffrey T. Gibbs.