On Friday, Benjamin Moloise, a 30-year-old black South African, is scheduled to be hanged in Pretoria. He has been described in news accounts in this country as a poet and as a political prisoner, but he is not about to be executed because of his writings or his opposition to the government. The penalty was imposed because he was convicted of killing a black policeman.

Many governments, including our own, have joined in international appeals for clemency. The U.N. Security Council even adopted a resolution urging South African authorities not to carry out the sentence, and on Wednesday the State Department affirmed its opposition to the execution.

The United States would have been in a better position to make this case, however, if the sentence had been given because of Mr. Moloise's publications or political activity, since this country doesn't penalize either with capital punishment. But when the offense is the murder of a police officer -- a crime for which many states in this country would impose capital punishment -- we do not occupy the high moral ground. In cases such as this, in fact, the United States stands squarely with South Africa and the Soviet Union, the only large, white-ruled nations in the world that allow capital punishment.

The imposition of this ultimate penalty on Mr. Moloise is deplorable, but so is the sanctioned killing of dozens of Americans for similar offenses. The South Africans executed 115 convicted criminals last year; we have more than 1,500 on death row. Executions are occurring here with such regularity that they no longer command sustained interest or provoke the outrage that they should.

The hanging in Pretoria must be protested, but so should the execution in Florida, the lethal injection in Texas and the firing squad in Utah. Government- sanctioned killing for violations of the law, no matter how vile the crimes of those on death row, is no more conscionable here than it is 8,000 miles away.