In addition to standard sources - newspaper and magazine articles, books and public speeches - Mr. Dugger found a heretofore unpublished treasure. He obtained the transcripts of more than 500 five-minute radio commentaries Mr. Reagan wrote and broadcast between leaving the governorship of California in 1975 and announcing his candidacy for the Presidency in 1979.

The tone of these broadcasts, excerpts from which Mr. Dugger reproduces, is less guarded and more strident than the tolerant, kindly image Mr. Reagan has cultivated as President. ''Eighty percent of air pollution comes not from chimneys and auto exhaust pipes but from plants and trees,'' Mr. Reagan declared on the radio in 1979. Smoking marijuana causes sterility, he said in another broadcast. Eliminating the tax deduction for business lunches would deny ''the working man his bologna sandwich.'' People on welfare are ''permanent clients of a professional group of welfarists whose careers depend on the preservation of poverty.''

In a 1978 commentary, Mr. Reagan applauded the development of the neutron bomb, which would release much more life- threatening radiation and destroy less property than a fission bomb of the same size. ''Very simply,'' he told his listeners, ''it is the dreamed-of death ray weapon of science fiction. Now, some express horror at this, charging immorality. That is sheer unadulterated nonsense. Indeed the neutron bomb represents a moral improvement in the horror that is modern war.''

Because the material is new, the radio transcripts make for the best reading in the book by far. But researchers may want to concentrate on particular chapters, for nowhere else is so much documented derogatory information about the 40th President of the United States presented in such well-organized fashion.

Say, for instance, you want to dig up some dirt about Mr. Reagan's stand on civil rights. All you need to do is turn to Chapter 11, entitled '' 'All These Beautiful White People.' '' The chapter title, you learn, comes from a remark by Nancy Reagan at a Chicago fund-raiser during the 1980 campaign. Talking to her husband in New Hampshire on an amplified telephone hookup, Mrs. Reagan said she wished he could be there to ''see all these beautiful white people.'' Elsewhere in the chapter, you can find direct quotations from Mr. Reagan on why he opposed the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the open housing legislation of 1968.