It's becoming clearer what is going on. As clear as the white person who drove past the South African embassy last week wearing a Rebel hat and carrying a sign that read "Hang in there, Pretoria." As clear as Roy McKoy, who last week closed his Marshall, Va., restaurant rather than serve blacks. As clear as former attorney general John Mitchell's recent "Amos and Andy" crack and President Reagan's currently destructive engagement with South Africa.

It appears that a white nationalist movement is under way, and black people are faced with having to march once again. It's not just about South Africa. What's happening over there has been going on for years. It's about America, too, and the insulting manner in which the Stars and Stripes have been waved in the name of racism.

For some whites, it's obviously difficult to see what the problem is. Only blacks can know the bitterness that comes with this particular brand of hypocrisy, where the basic tenet of life in America, that all men are created equal under God, is a sham.

"People are seeing the way Reagan supports the white South Africans and the way he treats blacks here and are beginning to make a connection between the two," said Rep. Parren Mitchell (D-Md.), after making a court appearance on Tuesday following his arrest at the South African embassy the day before.

Some whites argue that South Africa is anticommunist, and say what's so bad about a little apartheid in the name of freedom? In all sincerity, this is a prevalent argument among Reaganites. Somebody should pray for them.

Until recently, it seemed that South Africa was confusing to blacks, many of whom had been raised to regard black Africa as a distant and dark land of Tarzans and dumb tribal chiefs. But the presence of so many members of the black middle class among those protesting at the South African embassy suggest a significant perceptual change on their part.

Slowly, consciousness about racial apartheid is being raised with daily pilgrimages to the nonviolent protest. A unique drum beat can be heard from Wall Street to warehouses, calling others to the front line in a new level of "direct action."

So far, only a few hundred people show up at the South African embassy each day. But that was more than in 1974 when Parren Mitchell led black longshoremen in protest against Rhodesian ships carrying chrome ore on the docks of Baltimore. And more than in 1976, when social activist Dick Gregory became the first person to be arrested while protesting at the embassy.

Inside the city's jail cells, another group of blacks awaits the arrival of those arrested at the embassy. "The issues are being well discussed in jail," said social activist Dick Gregory after spending Monday night in a holding cell. "They inmates are kind of expecting to see somebody new every day and after talking about South Africa with me. They wanted to know, 'Who's coming next?' "

Said Josh Williams, a local labor leader who was arrested with Mitchell and Gregory, "When the police and the prison guards said, 'We appreciate and respect what you are are doing,' my spirits were uplifted and I began to feel the message was getting through."

While in a holding cell, D.C. Del. Walter Fauntroy was asked by a fellow inmate why he was so concerned with South Africans when problems here are so bad for blacks.

Fauntroy said he talked to the inmate about the link between the loss of American jobs to the cheap labor pools of South Africa and high joblessness here. As steel imports from South Africa increase, for example, jobs in the steel industry here are lost.

The argument makes sense and provides a basis for broadening participation in the protest against South Africa. But as the demonstrations continue, there is increasing focus on the apparent racial solidarity of Reaganite whites and South African whites and the danger facing all blacks as a result.

"They are like teammates playing the same game on different fields," one protester said of the relationship between Reagan and South African Prime Minister Pieter Botha.

As ugly as it sounds, it's an idea with enough clarity to carry black protest in this country to a new level.