How bad can a man be whose idea of a fun evening is to go home, put on his 'jamas and watch "Little House on the Prairie"?

I have been asking myself that question about Ronald Reagan for some time, and I now have an answer in the form of another question. The other question is: can Ronald Reagan control his own right wing?

By himself, Reagan makes a pretty poor excuse for a menace. He comes on warm and friendly and with the decent instincts of the Midwestern small town. While he seems to lack truly intimate friends, nothing in his record announces that he is -- to cite qualities associated with three recent presidents -- mean, vicious or megalomaniacal.

As governor of California, he was far less silly than he sounded. His appointments were on the whole good appointments. He did no serious damage to the university. If he saved money on welfare, as he claims, it was in large part because he accepted provisions made by the Democratic majority in the legislature that -- by funding abortions -- drastically reduced the number of children on the public assistance rolls.

Even though he is often misinformed on details, his errors of fact turn out to be insignificant. For example, he was wrong in asserting that Vietnam veterans are not eligible for the benefits of the GI Bill of Rights. But the general point he sought to make was right on -- namely, that the country needs to do more to keep up its reserve forces.

For all those reasons, the efforts to paint Reagan as a black villain don't come off. They turn into quibbles about what he really said and really meant. They convince only the already convinced.

Still if Reagan-as-bad-guy is a myth, there really and truly is such a thing as the far right wing of the Republican Party. Its members adhere to a wide range of ideas obnoxious to a just government and a decent society. They are dead serious in their beliefs, and they line up behind Reagan with an intent to assume mastery of government and shape national policy.

In the economic field, the far right position is well defined. It is the position associated with Prof. Arthur Laffer of the University of Southern California. The "Laffer Curve" purports to demonstrate that the tax system is so inefficient that big cuts in business levies would actually yield more revenues.

That proposition is repudiated by almost all serious economists, including -- on "Meet the Press" this past Sunday -- former secretary of the Treasury George Shultz. As Shultz pointed out, unless tax cuts are closely linked with spending cuts, they would generate ruinous inflation. But the absolute need for such linkage is 'not acknowledged by the far right.

In foreign policy, too, there is an established right-wing position. It is a position rooted in blind ideological anti-communism and favored by many of Reagan's advisers. It finds expression in several disastrous notions.

One is the idea that this country should forget about easing tensions and deliberately engage the Russians in an all-out arms race designed to run them into the ground. Another is the notion that the United States should give Communist China the wet mitten because Peking lacks ideological purity. Then there is the conceit that the United States should resume development of anti-ballistic missiles -- a step sure to yield an unchecked arms race.

Reagan is not himself irrevocably committed to those ideas. If elected president, he could probably count on a Democratic Congress to kill some of the wilder follies. But he too would have to play a role. The president does, after all, make all the big appointments and initiate most of the policy, especially in foreign affairs.

So far, the evidence is that Reagan is not going to be particularly good at holding his right wing. He is easygoing and congenial and hates bickering. He is given -- as the case of the almost successful effort to unseat former senator Bill Brock as national Republican chairman demonstrates -- to letting things happen. Those are just the qualities to make a president the prisoner of a determined minority in his entourage.

As the campaign wears on, accordingly, Reagan bears close scrutiny. There is a need for him to show that he has the acumen, the physical vitality, the instinct for picking the good men required to hold in check the truly malevolent forces he would bring with him to what is still the most powerful office in the world.