President Reagan doesn't plan to stay in the Rose Garden during the fall campaign, but he is taking his Rose Garden with him.

While Reagan will be seen across the nation on the evening news, supposedly talking to the American people in front of carefully chosen backdrops, he will be effectively isolated from the give-and-take of real campaigning and from questions he might be asked by the traveling news media.

In the process of overprotecting the front-runner, Reagan's White House managers have co-opted the Secret Service for purposes that have nothing to do with the president's security, reduced reporters to the unwilling role of props and contemptuously treated the president as a communicator in constant need of a keeper.

When a president travels, he is accompanied by a small, rotating "pool" of reporters representing each segment of the media. The system rarely produces profound dialogues but does provide a framework for day-to-day exchanges between the candidates. Often, a candidate's answer to a sensitive question reveals more about his feelings or motives than does a carefully scripted response prepared by the candidate's staff.

In Reagan's case, his answers to many questions have been valuable. He is, on the whole, more inclined than many of his aides to talk candidly. For instance, he openly endorsed Nicaraguan "freedom fighters" at a time his spokesmen were pussyfooting around the issue of U.S. involvement against the Sandinista government. There are many such examples.

But Reagan's proclivity for answering questions makes his staff members nervous. In some cases, they are concerned that he will dive in over his head on an issue in which he is ill-prepared. Usually, as one White House official put it, the concern is simply that a forthright answer will "eradicate the theme of the day," decided in advance by the president's staff.

So, special effort is being made to keep Reagan away from the media in an election that his managers believe is his to lose. One of the things his staff is doing to prevent Reagan from losing is keeping the press pool out of the president's hearing range. As White House correspondent Maureen Santini of the Associated Press said, "We're being kept farther away than before. As a result, we have not been able to ask questions."

But the White House staff wants to be certain that visuals of Reagan are first-rate. Last week at Goddard Space Flight Center, photographers were allowed to approach the president while reporters were kept out of questioning range. When Reagan leaves for Camp David, as my colleague David Hoffman wrote recently in the Washington Journalism Review, engines on the president's Marine helicopter are revved so Reagan cannot hear questions.

The most questionable tactic is using the Secret Service for non-security purposes. This is a touchy question for reporters to raise in an era when presidents are prime targets of assassins and in an administration whose leader was shot and seriously wounded in an attempt on his life. The Secret Service, widely respected for its professionalism, acted courageously and wisely when Reagan was injured.

But the White House staff is trading on this reputation, and damaging it, when it diverts the Secret Service from protecting the president to providing what ABC News correspondent Sam Donaldson calls "political security." This happened recently in Sedalia, Mo., where the Secret Service allowed Reagan to shake hands with strangers but closed in quickly on reporters who tried to question him. The staff was particularly sensitive at this time because of Reagan's ill-starred joke about bombing the Soviet Union.

When the staff wants reporters near Reagan, it is a different story. The Secret Service parted like the Red Sea to let the press pool through in Hoboken, N.J., when Reagan's advisers wanted him seen appealing to Italian-American voters in a Roman Catholic church. These reporters have security clearances and passes issued by the Secret Service and frequently walk through metal detectors.

What is involved, as some agents acknowledge privately, is not security but political protection of the president. "They take their cue from deputy chief of staff Mike Deaver and Nancy Reagan and the others at the top," said Donaldson, a frequent point man for the press corps in asking questions that need to be asked. "When the staff wants reporters close, they're close. And when the staff doesn't, they're not. They have taken the Rose Garden on the road," he said.

All of this should be troublesome even to Americans who distrust the news media. Reagan holds news conferences less frequently than any other modern president. He sees fewer people than most presidents and delegates more authority than any of them. He is the most protected by his staff.

During a period when he supposedly is taking his case to the American people, Reagan is being deliberately isolated by a staff that wants to take no risks. How isolated would he be in a second term, when he and his staff would be beyond reach of the voters?

Reaganism of the Week: Explaining his deficiencies in mathematics to two students at Jefferson Junior High School in Washington last Monday, the president said, "If I confessed to you how far I was behind both of you in these examples, you'd know why we have a budget deficit."