Protesters against U.S. intervention in Central America gathered in front of the White House yesterday to sign a "pledge of resistance," a pact to commit civil disobedience if the United States attacks Nicaragua. It was a page out of the book used by sponsors of the protests against South Africa, and the numbers of both groups show that dissatisfaction with President Reagan's foreign policy is growing.

But it is strange that these two groups, fighting against the same administration, could be so fundamentally different. Most of those opposed to intervention in Central America are white, while most of those who protest against South Africa are black.

Herein is a weakness that is sure to be exploited -- if it isn't being exploited already.

Although two out of every three Americans say they oppose escalating the war in Central America, Reagan continues to pick at the region with untold amounts of covert activity. And while no American favors apartheid -- so the polls say -- Reagan can rationalize the shooting deaths of 19 unarmed blacks by South African police by simply saying that "blacks policemen participated in the shooting."

How can he get away with this?

The answer must lie in the inability of Americans -- blacks and whites -- to come together and denounce the entire Reagan policy of supporting inequality and oppression -- not just in South Africa one day, Central America or the Philippines the next.

The American role in South Africa is not that different from that in many parts of the world: We are propping up dictators. Our leaders are financing oppression -- with our money.

Frankly, there are more whites involved with the protest against South Africa than there are blacks visibly concerned about Central America. But even if race is a factor in protest selection for blacks, this makes no sense. If the United States invades Nicaragua, a disproportionate number of blacks will die there just like they did in Vietnam.

Some organizers of the Central American protests try to make excuses for black noninvolvement. They say blacks have more pressing problems -- such as youth unemployment, declining financial resources and and a drug abuse crisis.

But many of these problems stem from the economic choices of the Reagan administration -- the choice to finance wars abroad rather than the well-being of people at home.

As members of Congress buckle under pressure from Reagan and succumb to his propaganda, there appears to be only one way left to effect change: mass protests and civil disobedience.

The TransAfrica-sponsored protest at the South African embassy has shown the way. In its early days, when the protest was most effective, it included a solid biracial and bipartisan coalition. It was a broad-based grass-roots movement whose strength was in its diversity.

The results have been that South Africa, once a hard-to-imagine land on the other side of the world, is now familiar to most Americans. With knowledge about the policies of that country -- and the American role in financing them -- has come movement in city after city to pass legislation that prohibits investments in the racist regime.

And the struggle continues. A coalition of pacifist religious groups is asking for signatures on a "pledge of resistance." If the United States makes war on Nicaragua, then thousands of Americans will be prepared to "wage peace" through massive nonviolent demonstrations.

This is the first time that Americans have started mobilizing before a crisis. Given the inclinations of the Reagan administration, from the invasion of Grenada to the mining of Nicaraguan waters, this is not a premature act.

To make such actions effective, however, it should be remembered that the race of the oppressed -- like the race of the protester -- should make no difference in the quest for peace through equality and justice.