A master politican, one who understood the way Washington works as well as any operative ever did, once remarked in a moment of frustration:

"The most difficult place in the world to get a clear and open perspective of the country as a whole is Washington. I am reminded sometimes of what President Wilson once said: "So many people come to Washington who know things that are not so, and so few people who know what the people of the United States are thinking about." That is why I occasionally leave this scene of action for a few days of fishing or go back home . . . so that I can have a chance to think quietly about the country as a whole."

That was Franklin D. Roosevelt speaking, with rare introspection, during his first term in the White House. FDR took his own advice, but not just about going fishing. His forays into the country, and his reports back to the people on them, were spectacular political successes. He was always, a presence in the land.

Now we are seeing a much more visible Jimmy Carter. He comes over our TV screens at a carefully staged civil service reform forum in a northern Virginia high school cafeteria. He journeys to North Carolina in the tobacco country, after stopping off in Virginia to commission a warship, over the weekend. He moves on to New York City this week for a ceremony at City Hall on U.S. aid to the ailing metropolis and then, it's said, may take in a Broadway show in the evening. He heads into the Midwest the following week to talk to a farmers convention in Columbia. Mo., and later plans a trip to Columbus, Ohio.

Then he plans a vacation with a return to his roots in Plains and it appears, some leisure time in the West, perhaps, at one of the national parks.

As if this were not enough of seeing and being seen, the president spends hours of late with key elements of the national media hierachies - with Time Inc. and Washington Post-Newsweek executives. NBC commentators and later sessions planned with other network and publishing concerns.

All in all, a major effort for Jimmy Carter and in this age of high-powered public relations by his image makers. A Page One headline in The Washington Star underscores the campaign, and undoubtedly pleases the Carter people: "Carter Sharpens Image," it reads. "In Fairfax Defense of Civil Service Reform." The accompanying story speaks of a "new" President Carter "somberly presidential, carefully focusing on a few key issues, boldly calling attention to his successes and swiftly dealing with embarrassments."

A rave review, indeed. Whether it's deserved or not is something else, but clearly the Carter presidency now enters a critical period in an attempt to regain lost political support.

Cynicism runs so deep in Washington that anything Jimmy Carter undertakes is bound to be disparaged in many quarters. That's certainly true of his latest image-refurbishing effort. Our past history of big PR campaigns designed to sell piliticians - and particularly presidents - has left a legacy of deep, and justified, suspicion about image manipulators. In fact, one of Carter's strongest assets as a candidate was the belief that he didn't seem packaged and phony.

At the same time the very idea that a president now is able to travel the country without stirring the ugly rancor and bitterness of the Vietnam-Watergate period is a strong testament to a healthier political climate. Jimmy Carter has contributed to restoring a better national tone, and deserves credit for it.

His attempt, too, at reaching out to those whose job it is to communicate news and information to the nation surely can be nothing but helpful. From the beginning of his presidency the most laudatory things that have been said about Carter have come out of his appearances before small groups. Again and again, people of widely differing backgrounds and interests have emerged from those sessions impressed by the president's grasp of issues, range of information and demeanor.

Unfortunately, that has not been the case with many of his public performances, either in set speeches or the "town meeting" format that has been employed for him so often.

The latest civil service forum was in that vein. Whether succuding appearances of that kind will build stronger public support for him and his policies remains, of course, to be seen. The guess here is that they won't. Part of this is because they seem stiff and staged. But the real problems with them are more complex. In the end they don't change anything, and people know it. And they don't permit people to feel they really know their president. The stage props get between the audience, the people and the principal actor, the president.

There perhaps lies the most notable difference between Jimmy Carter's public appearances and Franklin Roosevelt's.

So much mythology has grown up around the Roosevelt presidential legend that one simple political fact has been overlooked. Roosevelt was, in the best sense, a very great educator, which remains the greatest challenge facing any public figure - and most especially any president. It wasn't just FDR's fabled personal style - the voice, the mannerisms, the method of delivery, the physical presence - that made him such a successful national leader. He had the gift of making people believe he was taking them into his confidence, completely.

The evidence for this lies buried in those official volumes of presidential papers gathering dust on so many public library shelves today. For there, compiled year after year, one finds an extraordinary record of public leadership. Read over the full texts of those FDR radio fireside chats over the years and you begin to understand why he had such impact.

What's striking about them in today's context is their freshness, their directness, their candor, and their consistent developing of a single topic in terms that everyone could understand.

"I want to talk for a few minutes with the people of the United States about banking . . . " was the way he began his very first one just a week after taking office. "I want to tell you what has been done in the last few days, why it was done, and what the next steps are going to be."

Those words established the tone and the framework for the others that followed, month after month, on subject after subject.

Each was quite specific - why trees would be planted in the great Plains so topsoil would not swept away again leaving a new dust bowl developing - and they promised no miracles, no panaceas.They provided information about what the government was doing, and why the president felt certain action was needed. Most important, the vast majority of Americans felt they understood their president; they had become a partner with him, and gave him their support.

They also provide a national model of leadership, not just for the days of radio in the incomparably different '30s but for the age of television in the image-conscious '70s.