"This museum belongs right there, it's perfect," Daley said.
Opponents say the Illinois Supreme Court has ruled against previous plans to build in Grant Park.
If passed by the plan commission, the city council will probably vote on the project in June.
Mayor Daley outlined the city's plan to build a $100 million Children's Museum in Grant Park Wednesday. He wants it moved, taking over the Daley Fieldhouse in Bicentennial Plaza and creating a destination, he says, for the so-called bridge to nowhere to lead to somewhere special.
"It'd be wonderful to walk across the bridge and to a wonderful museum that really respects the whole skyline, respects the vision of the park and everything else, doesn't intrude, no intrusion at all," Daley said.
The mayor argued that most of the new building would be underground, and both sides were invoking the name of Chicago icon Montgomery Ward.
"This project is consistent with the true spirit of Montgomery Ward," said Daley.
"It's a violation of the Montgomery Ward decisions and the lakefront protection ordinance, there's overwhelming opposition," said Peggy Fiegiel, Save Grant Park.
Fiegiel is with one of many conservation groups opposed to moving the Children's Museum to Grant Park. She says the Illinois Supreme Court has ruled four times against previous plans to build in Grant Park, and a coalition of conservation groups is prepared to file a lawsuit if it gets that far.
Mayor Daley said recently that he has the 26 votes he needs to win city council approval. But 42nd Ward Alderman Brendan Reilly, who is leading the opposition against the move, says six council votes have changed to his side within the past 48 hours.
"The votes do the exist to support building a museum in Grant Park today. I'm not saying that isn't going to change back and forth, my hope is that we can avoid a city council showdown," Reilly said.