Folksinger Joan Baez will perform in Harvard Stadium on Tuesday August 19, beginning the first concert series in the Stadium's 66-year history.

In a break with precedent, the Harvard Corporation agreed in late June to lend the Stadium for the series of four concerts, which are now billed as "Stadium '69."

Arrangement are not yet complete for the other three dates--August 26, Sept. 2, and Sept. 9---in the series, but a reliable source said yesterday that negotiations are underway with the "Peter, Paul and Mary" group and with black comedian Bill Cosby.

The "Stadium '69" series is being put on jointly by the Riverside Neighborhood Association, (a citizens' planning group in a neighborhood adjacent to Harvard) and the National center of Afro-American Artists in Boston. The tow groups will split the proceeds from the concerts: the neighborhood association will use its share to promote low-income housing in Riverside, while the center's share will go to promote black culture.

The concert series was to have begun earlier this month, but difficulties in completing production arrangements held it up.

Neither a date nor a performer has as yet been chosen for another upcoming concert in the Stadium. This concert will be sponsored by the City of Boston; the proceeds from this concert will help to defray the expenses of "Summerthing," Boston's summertime arts festival.

Special provisions for control of crowds and transportation to the Stadium are to be made for all five concerts.

In another Stadium development, the Boston Globe revealed that the Boston Patriots will play their 1969 season in Boston College's stadium not, as had rumored, in Harvard Stadium.

Harvard officials last spring denied the reports that the Patriots would play in the Stadium, but rumors persisted that the team would be temporarily let into the long-desired stadium if the state legislature approved a bill to give them a permanent stadium. The legislature has not yet done so.