President Franklin D. Roosevelt, using a pioneer recording machine he had built beneath the Oval Office, taped private conversations and meetings during an 11-week-period in 1940, a University of Washington historian disclosed today.

The conversations -- for the most part Roosevelt monologues -- range from a furious rejection of Japanese demands that the United States demilitarize Hawaii, to discussions of wielding a charge that GOP presidential candidate Wendell Willkie had a mistress.

Excerpts from transcripts of 14 news conferences and seven or eight conversations will be published in the February/March issue of American Heritage magazine in an article by Prof. R.J.C. Butow.

Butow told a press conference today that Roosevelt "was angry at reports that came out of a meeting he had held in the Oval Office in January of 1939, with the Senate Military Affairs Committee, when one of the senators reported the president having put the American defense frontier 'on the Rhine.' "

Roosevelt's irritation led him to order White House stenographer Henry Kannee to find a method of assuring accurate transcripts of Oval Office discussions and press conferences. Kannee, after failing with a dictaphone hookup, had an intermediary approach RCA's Gen. David J. Sarnoff, who coincidentally was already preparing an elaborate recording device.

Sarnoff had the machine's progress speeded up, and by August 1940 a secret padlocked room had been built in the White House basement to contain a machine recording sound on film stock. It was wired to a microphone placed either in the president's desk lamp or in his desk drawer.

Backed by a phalanx of scholars, Butow played excerpts of the FDR tapes yesterday. "They certainly weren't used to entrap anybody," said historian Arthur M. Schlesinger Jr., a Democrat and a Roosevelt scholar. "If anybody was entrapped it was Franklin Roosevelt himself. He dominates the tapes and nobody else gets in edgewise."

Indeed, the tapes testify to the power that was Roosevelt's. Expansive and dramatic, his monologues convey his complex leadership and his spellbinding intimacy. The tapes have the eerie sound of a time warp, as the muddy but unmistakable Roosevelt voice -- whimsical and nearly majestic, and less oratorical than the crowd-tuned symphonic instrument used in public address -- emerges through the technological disadvantages of a practically antediluvian instrument.

"Look here now," President Roosevelt says on the tapes, "the prime minister of Japan has just given out an interview which may or may not be true . . . in which he says that Japan would regard it as an act of war if we were to give aid and comfort to any of the enemies of Japan. Now, what d'ya mean?"

At this point Roosevelt begins an imaginary dialogue between himself and his opposition.

President as opponent: "What's the word 'attack' mean?"

President as himself: "I don't know. It's perfectly possible--not the least bit probable--I mean it's as Jack Garner would say--a 1-in-10 shot, that Hitler and Mussolini and Japan, united, might feel that if they could stop American munitions from flowing to England--planes, guns, ships, airplanes, ammunition and so forth--that they could lick England.

"Now, they might send us an ultimatum: 'If you continue to send anything to England, we will regard that as an attack on us.' " Roosevelt slams his hand on the desk. "I'll say: 'I'm terribly sorry. We don't want any war with you . . . Now all we can say to you is that, of course, if you act on that assumption -- that we're a belligerent and make any form of attack on us, we're going to defend our own--we're going to defend our own--and nothing further.' "

Roosevelt sat that day, Oct. 4, 1940, in the Oval Office with House Speaker Sam Rayburn of Texas and floor leader John W. McCormack of Massachusetts, but neither of them speaks very much at all on the tapes. Four days later, on Oct. 8, 1940, speaking to unidentified visitors to the Oval Office, Roosevelt discussed Japanese demands on American demilitarization.

"This country is ready to pull the trigger if the Japs do anything. I mean we won't stand any nonsense, public opinion won't, in this country, from the Japs, if they do some fool thing. Now this . . . fella a Japanese emissary contacting Roy Howard of Scripps-Howard newspapers wires to Roy and says . . . there will be no war with the United States--I'm quoting from memory--on one condition, and one condition only, and that is that the United States will recognize the new era in--not Far East but--the East, meaning the whole of the East. Furthermore, that this recognition--there must be evidence of it, and the only evidence of this recognition the United States can give is to demilitarize all of its naval and air and army bases in Wake, Midway and Pearl Harbor.

"God! That's the first time that any damn Jap has told us to get out of Hawaii! And that has me more worried than any other thing in the world . . ."

Of the eight hours of recording painstakingly retrieved by Butow and Marc Weiss, a Queens College professor who served as a sound expert for Judge John J. Sirica on the Nixon tapes during Watergate, most of the time is taken up by largely unintelligible recordings of Roosevelt press conferences, which were then held in the Oval Office.

Both Butow and Schlesinger believe that the primary function of the recordings was to have been to record those press meetings, but that the conversations were taped due to lackadaisical turnings-off of the huge machine in the basement.

Those conversations represent an hour and a half of recordings that were discovered, untended to, among the Roosevelt archives at Hyde Park. Their existence had been known since Harry S Truman first had the machinery removed from the White House in 1945. Personnel shortages had led to a lack of attention to the tapes, transferred to disc form in the library. Of the eight hours, an hour and a half is devoted to conversations of deep and vital authenticity that served to bring Roosevelt to life as other evidence has not.

His political acumen and electoral sense of gut-punching show up in an August 1940 discussion with presidential aide Lowell Mellett. The battle for Roosevelt's third term was a particularly hard one among the Democrats, and the president became more deeply concerned when the news reached him that the Republicans had gotten hold of potentially dangerous material for the election.

Letters that Agriculture Secretary Henry A. Wallace had written to Nicholas Roerich, a White Russian mystic, beginning "Dear Guru:" had reached Willkie campaign officials. Word was out that they might be used to ridicule the vice presidential candidate in the campaign. Roosevelt had the idea that the common insider's knowledge of Willkie's longtime estrangement from his wife and involvement with a New York mistress might be a good device to make sure the Wallace letters were kept private.

"We can spread it as a word-of-mouth thing, or by some people, way, way down the line. We can't have any of our principal speakers refer to it but the people down the line can get it out." He slams the desk. "I mean the Congress speakers, and state speakers and so forth. They can use the raw material . . . Now, now, if they want to play dirty politics in the end, we've got our own people . . .

"Now you'd be amazed at how this story about the gal is spreading around the country . . ."

Mellett dares to say something: "It's out . . ." Roosevelt seems entranced with the story.

"Awful nice gal," President Roosevelt says, "Writes for the magazine and so forth and so on, a book reviewer. But nevertheless, there is the fact. And one very good way of bringing it out is by calling attention to the parallel in conversation . . .

"Jimmy Walker, once upon a time, was living openly with this gal all over New York, including the house across the street from me . . . She was an extremely attractive little tart . . . Jimmy and his wife had separated -- for all intents and purposes, they had separated. And it came to my trial as governor of New York Roosevelt was in charge of investigating Walker and Tammany Hall on corruption charges -- before me was Jimmy Walker, nineteen hundred and thirty-two, and Jimmy goes and hires his former wife for $10,000, to come up to Albany on a Saturday . . .

"Jimmy was a good Catholic and he hadn't been to church in five whole years -- and he paid his wife $10,000 to go up there, to Albany, on a Friday afternoon after my trial had finished for the week -- we were to go on Monday. Jimmy had never spent a Sunday in Albany in his life, but Mrs. Walker comes up to Albany, lives with him, ostensibly in the same suite in the hotel, and on Sunday the two of them go to Mass at the Albany Cathedral together. Price? Ten thousand dollars . . .

"Now, now," Roosevelt says happily, "Mrs. Willkie may not have been hired, but in effect she's been hired to return to Wendell and smile and make this campaign with him. Now, whether there was a money price behind it, I don't know, but it's the same idea . . ."

Neither the Wallace letters nor the Willkie scandal was used in the presidential campaign. In November 1940, Roosevelt won his third term to the presidency and the machinery began its years of lying fallow until its dismantling in 1945.