Viewed through the prism of television, Ronald Reagan is the most open and accessible of presidents. Television casts him as a reassuring fellow who recurrently enters your living room as leader, advocate and friend.

On New Year's Day, the president was on screen with a taped message of optimism during the Rose Bowl Parade and later exchanging peaceful noises with Soviet leader Mikhail Gorbachev. On less celebrated days, Reagan often dominates network newscasts, where he is glimpsed at "photo opportunities" that seem more intimate on television than in real life.

But television is reality for Reagan, as the movie screen used to be. On television, he is the master of his material. And on pretaped television, which he prefers, Reagan can say whatever he wants without interruptions.

Behind the television facade, however, the president is increasingly isolated. With few exceptions, Reagan has been deliberately kept from public view since he rescued his tax-overhaul bill in mid-December.

When the president travels, he is accompanied by a small group of reporters known as the press pool. But the reporters are kept so far away from him these days that, as a pool report observed at Palm Springs, they are "almost out of shouting range."

Reagan's formal news conferences, where ignorance or inattention to detail can be troublesome, have become infrequent. He has held 32 news conferences during his presidency, including only six in 1985, which began with an attempt by his spokesman, Larry Speakes, to make them regular monthly affairs. Perhaps Speakes, also less accessible than he used to be, has succumbed to the pressures that go with his position. In any case, Reagan has not held a news conference since Sept. 17.

Journalists who believe that such calculated underexposure inhibits the ability of a president to govern gain no support from public-opinion polls. As he prepares to enter the sixth year of his presidency, Reagan's popularity is secure and the major items of his domestic and foreign policy agenda are very much alive. That is better than most presidents have done in their fifth year and better than many of us thought Reagan would do a year ago.

But for all of Reagan's successes, there may be hidden dangers in his public-relations presidency. Reagan maintains public support by striking a responsive chord of optimism with his fellow citizens, who are asked not to sacrifice but to enjoy the seemingly unending fruits of a freed marketplace that provides the good things of life.

Reagan's relationship with the people has prospered with the success of his economic policies but may not meet the test of the inevitable downturn. His popularity was at low ebb during the recession of 1981-82, which he conveniently blamed on his predecessor. Reagan's fortunes have soured in the farm belt, where economic conditions a half-century ago foretold the Great Depression.

Reagan's managers, and the president himself, seem untroubled by negative economic auguries. As always, Reagan spent his entire vacation with the very rich, safely cocooned from the problems of the farmers or other ordinary Americans.

The managers also may be out of touch. White House chief of staff Donald T. Regan, stung by accusations that he wants to be "deputy president" or "prime minister," has kept away from the press and kept the president away from the spirited encounter of diverse viewpoints that used to be commonplace at the White House.

The new national security affairs adviser, Vice Adm. John M. Poindexter, is a bright but military-minded paper-pusher who was away when administration spokesmen went up hill and down dale in their statements about the appropriate response to Middle East terrorism. Reagan was briefed largely on paper during this period.

Increasingly, the Reagan administration functions reflexively, with most of the work done by mid-level aides. The president has strong-minded Cabinet members at State, Defense, Justice and Transportation, but they penetrate the White House cordon only on special occasions, as Secretary of State George P. Shultz did when he objected to Reagan's order calling for widespread use of polygraphs.

Reagan remains the Great Communicator and a president with a well-defined and popular agenda. But his government often runs on automatic pilot, and he seems too distant from his subordinates' deliberations or the outside world's concerns to notice. Eventually, isolation is likely to extract a price.