IN AN EXECUTIVE order of last Sept. 9, President Reagan responded to public dismay over his policy of constructive engagement in southern Africa and began imposing economic sanctions on Pretoria. He also instructed the secretary of state to name an advisory committee on how to "encourage peaceful change." George Shultz has now named the committee, and instantly it becomes the wild card in the administration's Africa-policy hand.

Traditionally, presidents turn to advisory committees or commissions when they're stuck and need help to muster a consensus. With South Africa refusing either to make good on its good-neighbor pledges or to move resolutely toward dismantling apartheid, President Reagan certainly was stuck. Any new consensus that the committee is going to be a part of, however, must inevitably be in a very different place from where Ronald Reagan himself started out and from where many of his conservative constituents remain.

The chairmen of the new panel are former Ford administration Cabinet officer William T. Coleman Jr. and former IBM chairman Frank Cary. Among its 12 members are equal-opportunity advocate Leon Sullivan, foundation officer Franklin Thomas, civil rights leader Vernon Jordan Jr., union president Owen Bieber, university president Timothy Healy and former State Department official Lawrence Eagleburger. It's not a radical group, but it's surely not made up of lap dogs either. Howard Phillips of the Conservative Caucus was not far off when he said, "If this committee had been named by Jimmy Carter, it would have been criticized as too far to the left." It is to the administration's credit that it has opened itself up to being criticized and influenced by a group of independent-minded citizens on whom it has few political or ideological claims.

To be sure, the administration does not exactly speak, or whisper, in one voice. The State Department apring with some of his work.