In his first month in office as France's president, Francois Mitterrand has transformed the atmosphere and the politics of the Elysee Palace, the 18th-century mansion where he hosted Vice President Bush yesterday for talks that ranged from American interest rates to communism in Europe.

For Bush, undoubtedly the most, important change at the French "White House" is that Mitterrand brought four Coummunists there yesterday to sit as members of his new 44-member Cabinet. Transportation Minister Charles Fiterman, the senior Communist, was seated in a place of honor to the French president's left at the early-morning Cabinet session.

But for a visiting reporter who participated in an interview with Mitterrand last week in the new president's office at the Elysee, there were other, more subtle changes that echoed both Mittermand's attachment to France's political history and his determination to strike a new, open style of governing that will break with the image of arrogance that contributed so heavily to the defeat of his predecessor, Valery Giscard d'Estaing, on May 10.

Seated in an open, sunny office looking out over the residence's carefully arranged gardens two blocks off the busy Champs Elysees boulevard, Mitterrand delt with questions in a style as remarkable for its literary quality as for its political substance. As he explained his views on Israel's attack on Iraq's nuclear reactor, an invisible pen seemed to be swirling about his head, carefully measuring out the cadences and fluidity of his elegantly composed French. That he takes at least as much pride in the eight books he has written as in his political accomplishments was evident in the conversation.

The interview was held in a golden-hued second floor room that Mitterrand has established as France's version of the Oval Office. The room was used as a working office by Charles de Gaulle from 1958 to 1969 and by de Gaulle's successor, Georges Pompidou, until his death in 1964.

Giscard preferred the more secluded, shielded apartment located at the eastern end of the Elysee, which was built in 1718 for a wealthy French nobleman and which has been the offical residence of French presidents since 1873. During an interview with Giscard four months ago, a ticking dock reverberated loudly through the silence that enveoloped his office as the aristocratic and aloof statesman presented an analysis of world politics that was as intellectually compelling as it was distant and cold.

Mitterrand moves cordially toward a visitor ushered in with relatively little formality and quickly gets down to the business of the conversation. A man who in his up-and-down political career has frequently donned an impeentrable mask when dealing with journalists, Mitterrand now appears to have much to say and eager to emphasize his own down-to-earth, humanistic approach to national and world affairs.

There is a certain bemusement hovering about Mitterrand as he develops his political stance during the interview, a suggestion of whimsy and of acceptance of the arbitrary nature of history that befits a man who had sought the presidency twice before and lost. It is an air that contrasts significantly with the all-powerful, all-knowing attitude that Giscard projected, knowingly or not, as he attempted to cope with France's growing economic and social problems until voters ousted him.

This contrast could serve Mitterrand well as the unemployment rolls and inflation rates continue to rise even though Giscard is gone. Many political analysts in Paris compare Giscard's defeat to that of former president Jimmy Carter, another leader who took the responsibility for dealing with virtually all of his nation's problems in a personal, detailed manner and found that his fellow citizens held him responsible not only for solutions but also for the problems themselves on election day.

Some of Mitterrand's choices of aides to fill the offices nearest him in the Elysee also say a good deal about the new French president. Two of the most controversial have been his international economic affairs adviser, Jacques Attali, and his foreign policy man, former guerrilla war theorist Regis Debray.

The actual extent of power that each has is unclear, but what is known is that both Attali and Debray love the same kind of probing and free-form intellectual discussions that Mitterrand seeks out in his private moments to hone a verbal mastery of ideas.