Republican Party leader Giovanni Spadolini told Italian President Sandro Pertini today that he will be able to form a new government and thus become the first non-Christian Democratic premier in the 35 years of the Italian Republic.

Spadolini, 55, an expert on church-state relations and a former newspaper editor, plans to form a five-party government that, along with his own small party, would include the Socialists, the Social Democrats, the Liberals and the Christian Democrats.

The five parties appear to agree on the substance of a 35-page program presented by Spadolini yesterday. It centers on the need to end corruption and on an emergency plan to deal with the country's 20 percent inflation rate and balance of payments deficit.

Nevertheless, Spadolini still could run into problems. Contrary to usual practice he has yet to draw up his list of Cabinet ministers. Most of the five parties involved, particularly the Christian Democrats and the Socialists, preferred to wait for the results of important local elections Sunday.

The division is not likely to be easy. The Christian Democrats have already said they expect their party's greater weight -- 38 percent in the 1979 national elections -- to be reflected in the composition of the new Cabinet. This has been interpreted to mean that they want more than half of the Cabinet posts.

Socialist leader Bettino Craxi has insisted that a new round of negotiations be held beginning Monday to "verify" the political consensus existing among the five groups.

The Republican leader, whose own party controls only 16 seats in the 630-member Chamber of Deputies, was asked to form a government a week ago when the outgoing Christian Democratic premier, Arnaldo Forlani, proved unable to put together a new coalition.

The Christian Democrats hold 262 seats in the Chamber of Deputies.

The Republican Party, a slightly left-of-center group, has a long reputation for integrity and Spadolini has been outspoken about the need to clear up the scandal over the P2, a secret Masonic lodge, which brought down Forlani's seven-month, four-party coalition three weeks ago.