A crowd of 200 jeering and stone-throwing militant black youths interrupted funeral services for black nationalist leader Robert Sobukwe yesterday, driving off Zulu chief Gatsha Buthelezi.

The youths converged on Buthelezi when he rose to give an eulogy for Sobukwe and, when he refused their demand that he leave, rushed at him, hurling stones and shouting, "Kill th pig" and "Sell-out."

His two bodyguards fired two shots, reportedly blanks, into the air, and Buthelezi, stumbling at one point, hurried from the stadium where the rites were being held and drove off.

The youths, though only a handful in the crowd of more than 4,000 who came to honor Sobukwe at his family's hometown of Graaf-Reinet, largely succeeded in dominating the service.

Other moderate figures quickly gave in to the youths' demand that they leave and two prominent white liberals cancelled their plans to speak.

The incident reflects the growing gap between the militants and those - blacks, racially mixed persons and whites - whom the militants denounce for their willingness to work within the system of racial separation imposed by South Africa's white-controlled government.

Two of the people asked to leave were Sonny Leon and the Rev. Abel Hendricske of the colored (mixed race) Labor Party. A third was M. Njisane, ambassador to South Africa from Transkel, which, like Buthelezi's Zulu region, has been set aside by the government for separate development under nominal independence.

The two white liberals who gave in to the militants' demands that they not speak were Helan Suzman, an out-spoken member of the opposition Progressive Party, and Benjamin Pogrund, editor of the anti-government newspaper, the Rand Daily Mail. They were allowed to remain.

Yesterday's attack on Buthelezi is the militants' most violent one yet against the Zulu leader. Last month he addressed a gathering of about 15,000 Zulu in Johannesburg's black township of Soweto without incident.

Buthelezi later accused the youths of making cheap political mileage out of the funeral and angrily told South African reporters that "I was prepared to die here. I came from brave stock. I am not afraid."

During the incident several people were hit by stones but no one was seriously injured. Three teenagers were brought to the local hospital with gun-shot wounds but it could not be determined if the shootings had occured at the funeral.

According to witnesses, most of the other mourners did not join th disturbance involving Buthelezi and did not appear to be concerned.

When the ceremonies began earlier in the day, the divergence between the older mourners, who had been the militants of the 1960s under the banner of Sobukwe's Pan African Congress, and today's young radicals first became apparent.

When the older people sang Congress songs, there was an obvious silence among the militants. Later, despite pleas from the funeral's organizers for silence, the youths sang freedom songs and chanted their slogans.

As the procession made its way to the stadium, the militants taunted South African police along the way and occasionally jostled them, witnesses said. There were no incidents. A police reconnaissance plans flew over the area but at the stadium police remained at a distance, not interfering even when Buthelezi was rushed.

Many of the young people came from the coastal town of Port Elizabeth where the unrest in the black community has not abated as it has in so many other towns in this country. This week two bombs exploded killing two people.

Other busloads of youths came from Soweto and the chairman of the Soweto Action Aommittee, Ismail Mkhabala, gave a radical speech urging the crowd to "hit back" at the authorities.

"We should not be running away from the guns; we should be carrying the guns," he said.

Among the mourners yesterday were U.S. Ambassador William Bowdler and his wife Peggy. Sobukwe, 53, died at his own home in Kimberly Feb. 25 of lung cancer.