THE TIME CAPSULE is a wonderful notion.

The idea is to collect contemporary artifacts, put them in a capsule and bury it so that future generations -- or maybe visitors from outer space -- will know something about the way we live. As for us, we're lucky in having our very own living, breathing time capsule -- a man who incorporates most of the values, if not the thinking, of the 19th century. Unfortunately, he happens to be president of the United States.

When it comes to foreign policy, for instance, the president has shown he has an outdated view of the world in which hostile forces come always from outside to topple governments. His mind is cluttered with battles, with large armies, with amphibious landings -- with a melange of Tobruk and Normandy, Inchon and The Bulge. He evidently thinks this is the danger Saudi Arabia faces and he has, in response, placed the shield of American military might around it. "I don't believe it will fall into enemy hands . . . " he said of Saudi Arabia and, anyway, he would not let that happen.

Just how he would stop it is another question entirely. The enemy that Saudi Arabia faces is not only Iran or the Soviet-backed regime in South Yemen. It is, paradoxically, both the 20th century and the 19th. The enemy, in other words, is the danger of not modernizing fast enough and, at virtually the same time, modernizing too fast. An absolute monarchy such as the Saudis have is an anachronism. This is a danger. Taking a feudal, third-world society into the 20th century is also a danger.

The fall of the shah and Iran's head-long leap backwards into a reactionary society ruled by religious bigots shows what can happen when you take the mullahs off the farm and show them the lights of Tehran. They get nauseous and cause governments to fall. The attack by religious zealots on the mosque at Mecca is yet another example that not everyone thinks happiness is running water and a pop-up toaster.

Reagan, however, does not seem to take these movements into account. To him, the danger is always from outside, specifically from Moscow, and it is to blunt this threat and the threat of Russian surrogates that, for instance, AWACS are supposed to go to Saudi Arabia. What good they will do against mobs in the street Tehran-style or contemporary zealots coming out of the desert, Mecca-style, is a total mystery. No matter. Nineteenth century dogma holds that the danger is from without. Twentieth century knowledge says that sometimes it is, and sometimes it ain't.

Similarly, when it comes to crime, the president could have been almost any 19th century preacher railing against crime, immorality and the rest of that stuff before sociology, psychology and even economics came along to complicate matters. Reagan virtually rejected the notion that a person can be rehabilitated or that environment contributes to crime. In rather stark, almost Calvinistic tones, he set out a blunt, primitive, theory of criminology: There are good guys and bad guys and anything more than that is sheer sophistry.

"The solution to the crime problem will not be found in the social worker's files, the psychiatrist's notes, or the bureaucratic budget," the president said. "It is a problem of the human heart, and it is there we must look for an answer." Thus did the president not only give the back of his hand to the social sciences, he also rejected the wisdom of Father Flanagan, the founder of Boys Town, who said, "There are no bad boys. There is only bad environment, bad training, a bad example and bad thinking." For the president to reject Sigmund Freud is one thing. To do the same to Spencer Tracy is beyond imagination.

When it comes to the causes of crime, it is obvious that the social sciences know very little or, at best, not nearly enough. But the fact that knowledge has come slowly and often painfully is no reason to tear up the textbooks and announce that we know nothing.

When it comes to both crime and foreign policy, we know more than we did in the 19th century, even if it is the humbling knowledge that we know very little at all. That, though, is no reason to look to the past for solutions, to reject reason and knowledge in favor of nostalgia and bromides. There are, after all, some things we do know. For starters, we know better than what the president has been telling us recently.