THE PRESIDENT--any president--tends to pall on

us after a bit through sheer overexposure. He becomes so hackneyed, as he pops up on the news night after night as a talking head, so profiled and scrutinized and analyzed by the columnists and the commentators, that long before he has reached the stage Ronald Reagan is at, with almost three years gone by in the White House, there is precious little more that any of us think we need to know about the man.

We have got to know his walk and his wave, we've heard his big speeches and his little jokes, several times over. We seem to know his family better than we know our own, and we've read his life story over and over again. Like him or loathe him, our minds, by now, are made up.

That is why it takes a writer with unusual temerity to come out with a new book on Ronald Reagan at this stage, and to claim that you have a mass of new material on the man and his beliefs. Yet that is just what Ronnie Dugger, Texas maverick and no stranger to temerity, has done.

There is nothing clandestine about Dugger's quarry of new material, though Reagan's staff has done its best to play it down. The material consists of transcripts of several hundred five-minute radio spots that Reagan broadcast after he left Sacramento in 1975; a series that ended the day he announced for president in 1979.

There can be no doubt whatever that these broadcasts express Reagan's own personal, instinctive attitudes to the important foreign and domestic issues of the day, as opposed to cooler or more cautious or veiled attitudes he may have been advised to express then or later.

Reagan himself, in the last of the broadcasts, states that he wrote them all with his own hand. "I've scratched them out on a yellow tablet in airplanes, riding in cars, and at the ranch when the sun went down."

They reveal him as perhaps a cleverer man than most reporters think he is. You may accept neither his premises nor his conclusions, but you will conclude, I submit, on reading these scripts, that Reagan writes better than you would expect. He has a sure sense of how an issue can be turned, sometimes twisted, to his advantage. And he has a real flair for one-liners.

The transcripts also reveal--and this is the heart of Dugger's contention--a harder, nastier political style than that of the relaxed, tolerant personality Reagan has so carefully cultivated in the White House.

That, no doubt, is why the Reagan campaign successfully hid the transcripts from the national press during the 1980 campaign, according to Dugger--though it has to be said that most national reporters were by then so terminally unimpressed with Jimmy Carter that there was no unseemly stampede to delve into Ronald Reagan's past.

"He was presenting himself to the country as a moderate," this is Dugger's key charge, "but these transcripts show that deep down he was a hardline right-wing ideologue with fully formed and recently expressed prejudices on all of the outstanding issues of the day."

The transcripts contain too much that supports this harsh judgment. All the clich,es of the Californian radical right are trotted out without inhibition.

"Eighty per cent of air pollution," the president believes, "comes not from chimneys and auto exhaust pipes but from plants and trees." Banning pesticides like DDT leads to "political pollution." Smoking pot leads to sterility.

The social attitudes revealed are uniformly indifferent to the old, the poor, the weak, and always coincide with the interests of the rich, corporations, and the financial Haves. The president is more moved by "the injustice done to Allan Bakke" than by the plight of those on welfare, and it is "demagoguery" to believe that income taxes should be progressive, that is, should increase with the size of incomes.

So what else is new? More surprising, and more unpleasant, is the president's habit of using the sly, indirect way of the propagandist, using code language to suggest more than he quite says right out.

He does not explicitly advocate the death penalty, for example. That would sound too bloodthirsty. Instead he quotes with approval the father of a murdered man who says, "after two years the murderer of my son goes free, but my son is dead." Because the late senator Joe McCarthy did not start to make his unsupported allegations about communists in government until after Alger Hiss had been charged with perjury, it does not follow, as Reagan implies, that those who oppose McCarthyism believe that the Cold War existed only in the minds of reactionaries.

Reagan also uncritically adopts some of the sillier canards of right-wing publicists and scaremongers. He even endorses the absurd suggestion that Orlando Letelier, exiled Chilean minister, had been killed by "his own side," --that is, by Marxists--when a secret agent of the Chilean junta has been convicted of the crime by an American court.

There is a good deal of old-fashioned chauvinism to be found in the broadcasts. The Caribbean, Reagan concluded because Michael Manley was prime minister of Jamaica, "is rapidly becoming a communist lake in what should be an American pond." What should be? The Caribbean basin? The Atlantic? The whole great gulf of ocean itself?

Most disturbing of all are the attitudes expressed towards the Soviet Union and to d,etente. Reagan's "solution" for the problem, on October 29, 1975, is worth quoting. It is an important text for interpreting American policy in the era of 1984.

"If we believe the Soviet Union is hostile to the free world--and we must or we wouldn't be maintaining a nuclear defense and continuing in NATO--then are we not adding to our own danger by helping the troubled Soviet economy? But isn't there also a moral issue? Are we not helping the Godless tyranny maintain its hold . . ."

"Maybe there is an answer--we simply do what's morally right. Stop doing business with them. Let their system collapse."

What if it doesn't collapse?

Ronnie Dugger takes this and other texts, and supplements them with other quotations from Reagan to show how deeply his policy towards the Soviet Union is rooted in the "devil theory." Reagan has not hesitated to say, in radio broadcasts or elsewhere, that the Soviet Union ought not to be a member of the United Nations, that d,etente is "a strategem," and to hint broadly that the Soviet Union was responsible for the assassination of President Kennedy.

With immense labor, over the whole field of domestic and foreign policy, Dugger has followed the same method, using the new evidence of the radio scripts to lay bare what he maintains are the president's real beliefs, carefully scraping away the accretion of diplomatic vagueness with which they have been overlaid in the campaign and in office.

The result is an extremely useful, and an extremely frightening book. Most frightening, again, is Dugger's analysis of the president's attitude to nuclear war. He shows how, at the time of the Vietnam war, Ronald Reagan was willing both to leave vital decisions about the use of American power to the military, and to hint, without quite saying in so many words, that if he were in the White House he would use nuclear weapons to win the war.

But Dugger goes farther. He argues that, considering the "plain facts," one must "consider reaching the conclusion that Ronald Reagan is the leader of elements in the government who want the United States to obtain a first- strike capability." If the Russians think the United States is planning a first strike, Dugger asks, what are they doing about it? Planning a first strike themselves, of course, is his answer.

Measured against that thought, as Dugger ends his book by saying, "Social Security, medicare, civil rights, the ERA, food stamps, unemployment and federal education can wait if we have the time to wait; everything can wait except the question of whether we have more time."

It is a devastating portrait of the president. That does not make it a wholly persuasive book. For one thing, ideas and attitudes are attributed to Ronald Reagan and to the "Reaganists" that are in fact rather general in certain circles and certain sections of the United States.

More to the point, as Dugger himself recognizes in his introduction, not all Reagan's ideas are mistaken. His reaction against the New Deal, as Dugger says, would not have taken him to the White House unless it expressed authentic grievances, genuine second-thoughts about what had been accepted wisdom, real pain experienced by those who had not been preferred targets for the benevolence of the liberal system.

It is true. but that does not make the real Ronald Reagan, revealed behind the mask of amiability in his radio scripts, any less profoundly disturbing.