The South African government had no official comment today on the formation of an alliance by the three major nonwhite groupings challenging the official policy of racial separation.

But comments in the pro-government Afrikaans-language press predicted that the alliance between the Zulus, the country's largest black, tribe, Coloreds (persons of mixed race) and Indians is doomed to failure.

The alliance formed yesterday by the leaders of the three groups called for a convention in March to formulate joint strategy against the racial policy of the white minority government and draft a new constitution for a nouracial South African state.

One of the leaders who took part in yesterday's meeting of the three nonwhite groups to Natal voiced fears today that the value attempt to destroy the alliance.

Sony Leon, leader of the Colored People's Labor Party, which represents 2.3 million Coloreds said he was convinced that the government would take steps "to prohibit us from even having talks together."

An alliance of 19 million blacks and Coloreds and Indians has always been feared by the 4.3 million white. Pro-government newspapers here are emphasizing that the well-organized Zulus would dominate the alliance and that the Coloreds and Indians would do better by siding with the government.

Ironically the alliance faces opposition among the blacks at the two extremes of the political spectrum. The left-wing urban blacks influenced by the black - consciousness movement who oppose the the Zulus' effort to work within the system. At the same time conservative homeland leaders fear their authority would be undermined by the numerous and well-organized Zulus.