Farley Mowat is dangerous. He is pro- wolf and worse, pro-seal, pro-owl and pro- deer. Among humans, he is pro-Eskimo, pro-Viking and pro-Siberian. His politics are Newfoundland-revanchist. He has admitted to fear in wartime.

Worse, this man is a writer. His weapons are words. They cross boundaries, evade radar and can be shot down only by better words, of which there are few. Sometimes they become images on film and penetrate where even words will not go. Among his many Canadian and literary awards is the Stephen Leacock Medal for Humor -- the ultimate weapon, for which no defense is known.

Small wonder the Immigration and Naturalization Service proscribed him as one of the 40,000 dangerous characters in its "Lookout Book," to be kept out of this country at all costs under the 1952 McCarran Act. If he were a terrorist, Communist, Nazi or cocaine distributor -- all a dime a dozen -- INS could afford to look the other way. But this man is a writer. He was going to Los Angeles to promote his book, "Sea of Slaughter." At least that's his story. He was probably going to sell it to movie producers, like "Never Cry Wolf."

Fortunately, the INS caught him red- handed with an airline ticket in Toronto Airport and banned him. Never mind that Canadians don't need passports to enter this country. Never mind the friendship between Canada and the United States, the greatest free movement of goods and people and capital between two countries in the history of the world. Never mind the unfavorable publicity for the United States. Never mind the ridicule heaped on the Reagan administration ("SS troops were victims; seals are killers").

You might almost suspect the Commies had penetrated the INS for it to come up with such a harmful move to U.S. interests. Or that his publisher had. It couldn't buy this amount of publicity. But if we let such a man into this country, he would probably only try to save the rockfish. He is beyond redemption.

You might think the INS is like the little boy who cried "Wolf!" But how could it do otherwise? When the author of "Never Cry Wolf" is coming, it must cry "Wolf."