A Reagan appointee to an international broadcasting board yesterday acknowledged he belongs to an all-white country club, owns extensive holdings in South Africa, recently spent 12 days there at the expense of its government and is a former director of a group that financed research into theories that blacks are genetically inferior to whites.

Thomas Ellis, a top political ally of Sen. Jesse Helms (R-N.C.), also said he opposed school integration in the 1950s and circulated handbills claiming that Gerald R. Ford wanted a black running mate during a critical 1976 presidential primary.

Under sharp questioning, however, Ellis said: "I do not believe in my heart that I'm a racist."

Sen. Joseph R. Biden Jr. (D-Del.) raised the issue during a Senate Foreign Relations Committee confirmation hearing, arguing that unless Ellis could explain his past activities Soviet propagandists might seize on his appointment as a racist one.

Ellis testified that his views on race had changed. He said some research now suggests to him that blacks are genetically superior to whites.

However, when asked if he now condemns racial apartheid, Ellis said he could not "second-guess" the South African government. He said it was doing the best it could under a bad situation. This and other statements led Biden and Sen. Paul E. Tsongas (D-Mass.) to call for President Reagan to withdraw the nomination.

Ellis was nominated to the Board for International Broadcasting, a prestigious panel that oversees Radio Liberty and Radio Free Europe, Feb. 8. But Republicans, fearing an embarrassing confirmation fight, delayed a hearing until yesterday.

The most damaging part of Ellis' background concerned four years he served as one of two directors of the Pioneer Fund, which financed research into theories that blacks are genetically inferior to whites. Ellis testified that he knew almost nothing about the the foundation and became a director only because an old college roommate asked him to.

Ellis, 62, said he resigned in 1977 after newspaper articles reported activities of the fund. He said he felt his involvement might prove politically embarrassing to Helms.

A Raleigh attorney, Ellis managed Helms' 1978 election campaign as well as Reagan's 1976 victorious North Carolina primary campaign. During that primary, he circulated hundreds of handbills that were printed to show, through certain headlines, that Ford, then president, favored a black as a running mate.

Ellis chairs the National Congressional Club, a conservative political action committee closely tied to Helms. Yesterday Helms defended Ellis as a "dedicated American."