A Vatican official who is coordinating arrangements for the American visit of Pope John Paul II met with both church and government leaders here yesterday to discuss plans for the pontiff's October visit.

Church leaders said that a formal announcement of the pope's travel schedule in this country is not expected for another week.

Bishop Paul Marcinkus, who is president of the Vatican bank as well as coordinator of papal trips, conferred yesterday and Wednesday both with officials of the Washington Roman Catholic Archdiocese and with White House and State Department staff members.

While church officials stress that plans are not firm, the pope is expected to arrive in Boston on the afternoon of Oct. 1, and has been asked to celebrate a public mass there that same afternoon.

On Oct. 2 -- the only date which is firmly scheduled -- he will address the General Assembly of the United Nationa. New York Archdiocesan officials have proposed that he also hold masses in both Shea and Yankee Stadiums, that he tour either Harlem or the South Bronx and also make a public appearance at Battery Park at the southernmost tip of Manhattan.

He is expected to make a brief stop in Philadelphia and spend a longer time in Chicago, the nation's largest archdiocese, where he will probably meet with a gathering of the American church hierarchy. Chicago church leaders are also proposing a public mass at a site which would accommodate from 250,000 to 1 million people.

He is expected to wind up his American tour in Washington -- probably Oct. 6 or 7 -- with a massive religious service on the Mall. It is also anticipated that he will call on President Carter at the White House.

Marcinkus, a priest of the Chicago Archdiocese, has already conferred with New York church leaders and is expected to visit Chicago after visiting Boston today.