One of the continuing puzzles about President Reagan is the quality that his intimates see in him that makes them feel he needs to be shielded from the outside world.

Any president needs security protection against assassins and terrorists, of course, and this one -- who has been the target of one murder attempt -- is, thank goodness, getting the best protection the skilled Secret Service can provide.

That is not what I am talking about. I am talking about the political protection and insulation in which Reagan has been wrapped -- often to his seeming disadvantage -- by a succession of political aides and advisers.

The sheltered nature of his current campaign has been well-discussed. The sites -- and often the crowds -- for Reagan's events have been carefully screened. In negotiations for debates, his handlers made it clear they did not want genuine debates, but forums where moderators and panels of questioners stand between him and his opponent. When he has a press conference -- well, he has not had one since July, so there is no need to finish the thought.

But this is not a special condition imposed during the campaign. It has been a characteristic of his presidency. Rarely if ever has Reagan been left unguarded and unattended to deal with issues and situations on his own.

Foreign diplomats and members of Congress have found that an invitation to meet with this president is really a summons to a committee session, with the president surrounded by members of his staff, his Cabinet and, of- ten, Vice President George Bush.

As they describe the sessions, the president often does little more than offer an opening word of welcome, then settles back to listen as the others discuss the matter before them.

Even when journalists are invited in to hear the president talk informally, we find that several members of his top staff -- busy people with work of their own to do -- draw up their chairs to the table. There is, in short, a lot of hovering around.

It has never been clear to me just what it is that the people in this protective phalanx believe they are protecting. Reagan is a fine conversationalist, perfectly at ease with people. There are no visible signals that pass from the aides to the president in these sessions, nor does he seem to need their instruction to know what to say.

Yet they always seem poised to intervene -- as if he were going to need help.

Some people who have worked for Reagan over the years, and no longer do, tell me they believe the president has a strong distaste for any kind of personal confrontation. He does not like to be contradicted or even closely questioned on his views, they say.

That's understandable. Most of us don't savor the experience -- even if it's one of our own kids saying, "Pop, you don't know what you're talking about."

But sensitive souls with thin skins don't usually become union presidents or conduct contract negotiations, as Reagan did when he was head of the Screen Actors Guild. They don't go into politics and become governor and president.

The "shrinking violet" theory is implausible.

The other theory I have heard from these former intimates makes more sense. It is that those who work with Reagan quickly come to understand how little his policy views rest on information or facts -- and how much they rely on his own instincts and long-cherished beliefs.

Even to an outsider, it has long been obvious that policy analysis is not Reagan's favorite indoor sport, or even close to the top of the list. The books on the Reagan presidency by Lou Cannon, Strobe Talbott and Laurence I. Barrett abound with anecdotes illustrating the incumbent's often shaky hold on relevant information.

There are a couple of good reasons why the inner circle of advisers would want to shield that kind of president from outside contacts. It makes it easier for them to channel the flow of information to him in ways that move policy in the direction they want it to go. And, as people to whom information and facts are important (indeed, the staple of their business, as of mine), they may have an exaggerated notion of the importance of concealing from the public Reagan's own indifference to expertise.

An outsider cannot judge the extent to which Reagan's conduct of the presidency is hampered by his distaste for close analysis of policy questions. After almost four years in office, he is entitled to be judged by the results, as voters are now doing for themselves.

But it is striking that so much of the energy of the top White House people -- a talented group, for the most part, who are carrying out their own responsibilities well -- is siphoned off to the task of shielding the man in charge. Whatever it is they know about Reagan, it is certainly something they don't want us to find out.