Opponents of Maryland Gov. William Donald Schaefer's plan to build two sports stadiums in Baltimore delivered petitions yesterday that they say contain more than enough valid signatures to put the issue on the ballot in 1988.

A spokesman for the secretary of state's office in Annapolis said that the signatures on petitions received yesterday have not yet been officially counted, but the stadium opponents said they now have at least 45,000 signatures on each of two stadium-related petitions.

They need 33,044 valid signatures of registered voters to bring the stadium question to a referendum. In early June, stadium opponents turned in more than 26,000 signatures on each petition, and they said there were 19,500 more on each by yesterday's deadline.

One petition challenges the selection of the Baltimore warehouse district in Camden Yards as the stadium site, and the other challenges the proposed financing of the stadium complex.

The state has maintained that the stadium issue is not one that can legally be placed before the voters, and stadium opponents have mounted a court challenge to that position. A ruling is expected in Anne Arundel County Circuit Court today or tomorrow, but the issue is likely to end up in the state Court of Appeals.