Like a Jonah deciding that he can fight the whale more effectively from the inside, the leadership of South Africa's second largest minority--the 2.5 million mixed-race "coloreds"-- has voted to accept a constitutional proposal that promises them at least a muted voice in a parliament in which whites will remain supreme.

The vote was either an example of political pragmatism, getting what you can when you can; a case of political perfidy that rewarded the white supremacist government's divide-and- conquer approach to its racial dilemma; or fundamentally suicidal.

It depends not only on who is making the assessment but also on how one assesses the future of that race-torn country.

A key provision of the proposal is for a three-chamber parliament, comprising separate branches for coloreds, Indians and the ruling whites. The Indian Reform Party is expected to decide later this month whether to cooperate in the plan, which proposes no change whatever for the disfranchised blacks, who constitute nearly three- quarters of the South African population.

That arithmetic is at the heart of the dilemma. If you believe that whites will be able to maintain total control indefinitely, then it might make practical sense for the coloreds and Indians to accept even a small step in the direction of political cooperation with them. But if major change--peaceful or otherwise--is as imminent as many observers believe, last week's decision may constitute exchanging frying pan for fire.

Gatsha Buthelezi, chief of the six- million member Zulu tribe, South Africa's biggest, said as much in his remarks urging rejection of the parliamentary change. "For the colored community to accept proposals which exclude their African compatriots would be a disaster for them and for everybody," he said. "It would be interpreted, rightly or wrongly, as your ultimate abandonment of Africans as your fellow countrymen and fellow blacks. The colored and Indian people will become, in our eyes, second-class enemies. One sometimes respects one's large enemy but seldom his little runners and camp-followers. They are without honor at all."

Naturally, the colored leadership sees it differently. The Labor Party's national chairman, David Curry, called it "politically expedient to use this opportunity to get what we want. South Africa is irreversibly in a process of reform. We must get in there and make ourselves part of the process."

He and other leaders vowed to "continue to strive for full participation of blacks." It's hard to see how. Under the proposed tri-chamber parliament, coloreds and Indians can pass no legislation without white endorsement. And while they have the theoretical ability to block certain legislation, any measure thus blocked will be passed along to the white-controlled President's Council, whose decision will be final.

In truth, if the colored and Asian leaders were interested in promoting full political participation for non- white South Africans, they might have done so more effectively by sticking together, which they had managed to do surprisingly well for the past several years.

By buying into the charade of this constitutional proposal, they not only delay political participation for blacks, but they also risk handing the white- ruled government unwarranted credit for moving in the direction of racial justice while reaping only the most marginal of benefits for themselves.

It must finally occur to them, as it did to Jonah, that their interests and the whale's are not exactly similar.