A day after the “Daily Show” star Jon Stewart announced plans to stage an ambitious public rally to counter what he identified as extremists on either side of the political spectrum, specifics were in short supply on Friday, with most of the details still to be worked out.

On Thursday night, Mr. Stewart told his television audience that the show had secured the National Mall in Washington for what he called the “Rally to Restore Sanity” on Oct. 30. He later labeled it a “Million Moderate March.”

The purpose, he said, is to present an alternative to what he called a minority of 15 percent or 20 percent of the Americans who have dominated the national political discussion with extreme rhetoric. Mr. Stewart tarred both parties with that charge, citing the attacks on the right accusing President Obama of being everything from a socialist to un-American and on the left accusing former President George W. Bush of being a war criminal.