Italian President Giovanni Leone resigned yesterday folowing public charges of corruption and an unexpected call for his ouster from the powerful Italian Communist Party.

Leone's resignation six months before the end of his seven-year term in December came in response to mounting political pressures set off by allegations of Leone's involvement in tax evasion and trade kickbacks including a $2 million Lockheed bribery case.

In announcing his resignation in a nationally televised broadcast last night, the 69-year-old Christian Democrat professed innocence, saying to the nation that "for the six and a half years you have had an honest man as your president."

The Communists' decision to join forces with several Italian groups seeking Leone's ouster appears to have been crucial. Earlier yesterday Leone had asserted that he had no intentions to step down.

The unprecedented move marked the first time since the fall of facism that an Italian president has been forced to resign. It also threatened to create new political confusion for Italy following the formation of a Communist-backed government and the kidnap-murder of former Premier Aldo Moro earlier this year.

The resignation was effective immediately with the Christian Democratic president of the Senate, Amintore Fanfani, 70, taking over as interim head of state.

According to the Italian constitution, elections for a new president must be held within 15 days. Leone's successor will therefore be elected before the end of June by the National Assembly, a 1,011-member body composed of Italy's two houses of parliament and representatives of its 20 regions.

Although largely ceremonial, the post is regarded as a potentially key position since the president makes many important appointments, is the commander of the armed forces, and most importantly can dissolve parliament after conferring with its leaders.

Leone, neapolitan lawyers and politican, took office in December 1971 after being elected by the National Assembly on the 23rd ballot. However, he has operated under a cloud of suspicion ever since early 1976 when it was revealed that the had close ties to two lawyer brothers who acted as intermediaries in Italy's $2 million Lockheed scandal.

Since then he has been the object of frequent press attacks including a 1978 best seller, the author of which has been charged with defamation, and a three-part series this month by the leftwing weekly Espresso accusing him of tax fraud and corruption.

The articles, the last of which appeared yesterday, include as yet unsubstantiated charges of attempts at arranging trade kickbacks, tax evasion and illegal or unsavory real estate deals but were sufficient to set off an attack against Leone by several small leftist groups. They were joined by Republican leader Ugo La Malfa Wednesday and by the powerful Communists yesterday.

Eager to preserve the current politiclal punture in which they play a major role, the Communists in the past have repeatedly sought to protect Leone. But their heavy losses in recent local elections and widespread disregard of their official support for a party-financing law in a popular referendum held last Sunday, apparently convicted them that it was worth risking political stability to regain their former, politically profitable anti-corruption image.

In a tersely worded statement issued yesterday afternoon, the Communists called upon Leone to step down "to disperse doubts and remove speculation around the highest office in the land."

For similiar reasons the Christian Democrats used similiar language yesterday and apparently made no attempts to block the resignation of Leone, who served briefly as a Christian Democratic premier in 1963 and again in 1968.

Leaders of the Christian Democratic Party, repeatedly accused of corruption over the last 30 years believe that they took the first major steps in acquiring a clean-hands image by refusing to deal with the terrorist kidnappers of Moro.

Party sources said yesterday that the results of this week's referendum which showed the limits of their influence as well as that of the Communists, indicated that "we have a long way to go." "If Aldo Moro's sacrifice is not to be in vain we can't risk being charged with a cover-up", a mid-level party official said.

Leone's decision to step down came two weeks before the onset of a six-month period called the "white semester" in which the president cannot dissolve the legislature and during which national elections cannot be held.

The nearness of that dealine has thus led to speculation that the charges against Leone, or at least their publication, may have been engineered by groups eager to leave the election option open at a time when, as the recent local elections showed, the Christian Democrats and Socialists did well while the Communists sufferred heavy losses