President Reagan's secret weapon is that he is a man of conviction whose views and actions often transcend the political concerns of his subordinates.

Out of touch with civilization, not to mention his White House staff, during much of his August vacation on his mountaintop ranch, Reagan has nonetheless put his stamp on decisions that deeply divide his advisers.

My colleague Mark Shields once observed that the term "Great Communicator," ostensibly complimentary, is often used derisively by Reagan's critics to imply that his popularity is based on his television presence or practiced skill in reading a script. In fact, Reagan is that rare bird among politicians who has formed a following that values him as man of principle who will not sway with every passing breeze.

The assets and liabilities of Reagan's approach were on full display as the president's pleasant summer vacation passed into history. Deciding not to impose import quotas on a shoe industry battered into submission by foreign imports, Reagan defied the protectionist -- and largely jingoistic -- mindset sweeping Congress and much of the country these days.

Terming protectionism "both ineffective and extremely expensive," Reagan pointed out that it is "a crippling cure, far more dangerous than any economic illness."

Reagan, a classic free trader, used almost the exact description of protectionism when I interviewed him 17 years ago. He has believed in the dangers of protectionism far longer than that, since his New Deal boyhood a half-century ago when he learned that high tariffs had been one of the contributing causes of the Great Depression.

Reagan does not easily forget what he learns, even when circumstances change. Long before Jeane J. Kirkpatrick wrote her famous Commentary article on "Dictators and Double Standards" during the 1980 campaign, Reagan was drawing distinctions between "authoritarian" regimes of the right and "totalitarian" ones, which in our time he considered synonymous with communist governments.

Reagan is always hostile to communism but gives his abundant optimism full reign in dealing with authoritarian governments, which he believes are giving way to a rising "freedom tide" of democracy. He counts small victories as large ones and is apt to interpret minor gains in civil liberties as signifying an end to political repression. This tendency has been encouraged by the legitimate example of El Salvador, which Reagan supported against his critics and whose government under Jose Napoleon Duarte has made him look good.

But South Africa is not El Salvador, and it is also not the American South of Jim Crow days, as Reagan's statements about its progress imply. Reagan has resisted learning about South African reality, and his naive belief about the inevitability of democratic evolution is abetted by the view that communism will triumph if the government of Pieter W. Botha fails.

Faced with demands to do something, Reagan has dug in his heels and convinced himself that the Botha regime is "a reformist administration." To support this thesis of "constructive engagement" with South Africa, Reagan claims credit for minor steps of progress, some of which occurred during the Carter years, while ignoring Botha's determination to prevent blacks from voting or having a say in the policies of their government.

Reagan is as little influenced on this issue by advisers who warn of political repercussions as he was in denying the shoe-import quotas. In fact, he has made it known that he intends to veto sanctions legislation even though he faces the almost certain prospect of having his veto overridden. The best the advisers have been able to pry out of him is agreement for some mild measures of disapproval that can be ordered by executive action.

In standing up to Congress and common sense on South Africa, Reagan is being true to his view of the world at the expense of the political wisdom of his foreign policy team. On shoe imports and South Africa, Reagan is demonstrating that strong convictions can be both a blessing and a curse.

Reaganism of the Week: Commenting on South Africa in a radio interview broadcast last Monday, the president said: "They have eliminated the segregation that we once had in our own country -- the type of thing where hotels and restaurants and places of entertainment and so forth were segregated. That has all been eliminated."