Rep. Paul Simon (D-Ill.) yesterday called the Reagan administration's contention that private and corporate support for the arts would be "revitalized" by cutting back federal funding "completely baseless."

"Far from supplanting private and corporate dollars, this federal money spurs private and corporate support that otherwise would not exist," Simon said yesterday during his opening remarks at a hearing held by the House Subcommittee on Post-Secondary Education, which Simon chairs.

A number of supporters of arts and humanities programs trooped past the subcommittee in the first of several hearings that will be held by different congressional committees over the next couple of months. And, like those heard yesterday, most will argue against Reagan's proposed 50 percent cuts of both the National Endowments for the Arts and the Humanities, for which President Carter requested $344 million. They described how federal funds spawned private funds, how federally funded arts programs revitalized downtown areas.

"In 1978, the NEA granted $5,000 for a three-day downtown festival in Richmond," Henry Marsh, the mayor of Richmond, told the subcommittee. "The $5,000 was matched by $40,000 and brought 100,000 people to our center city -- and still brings them back each year."

Referring to his July poll, Louis Harris -- the pollster and also the chairman of the American Council for the Arts -- said, "By 59 percent to 39 percent, a solid majority [of Americans] are willing to pay $15 more in taxes, if need be, to assist the arts financially. That is 20 times the amount now funded by the federalm government."

The subcommittee -- which also heard from Rep. Fred Richmond (D-N.Y.), founder of a new congressional arts caucus, among others -- will assess the impact of these proposed budget cuts and then report back to the full House Committee on Education and Labor.