The "Stadium '69" concert series--which weathered a brief legal squall yesterday--will begin as scheduled tonight with folksinger John Baez.

A Suffolk Country district judge yesterday threw out suits brought last week by a Boston Rock promoter, George Papadoupolos, who sought to stop the concerts, charging that their producers had not given him the credit he deserved.

The co-sponsors of the concerts--the Riverside Neighborhood Association and the National Center for Afro-American Artists--said that Papadoupolos had only been discussed as a possible producer for the series, and had not been instrumental in arranging it.

In all, Papadouspolos filed four suits--against the co-sponsors, against Harvard, which lent the Stadium for the concerts, and against Edward S. Gruson, assistant to the President for Community Relations, who arranged the loan of the facility. The suits against cosponsors and Harvard were thrown out yesterday; a hearing has not yet been held on the suit filed against Gruson.

Ticket sales for the Baez concert are "forging right ahead," a spokesman said last night. He declined to estimate how many were likely to attend the concert--"If I could predict that I'd make a fortune just predicting"--but added that "realistically, we're prepared for about 25,000."

While there will be no special transportation facilities for the concerts, about 100 Harvard, Boston, and MDC policemen will be on hand to keep order in the crowd.

Tickets for the concert are available at the stadium, Boston ticket agencies, and at the Afro-American arts center in Roxbury. The tickets are all priced at $2, which was one of Miss Baez's conditions for appearing at the stadium.