HARRISBURG — A plan to extend Pennsylvania's sales tax to the performing arts, museums, historical sites, zoos and parks is partly designed to shift the taxpayers' share of financing those activities onto their patrons, an architect of the proposal said Tuesday.

"The idea was to try to make it a user fee as much as possible," said Sen. Jake Corman, R-Centre, chairman of the Senate Appropriations Committee.

The plan, a late addition in the negotiations that yielded a deal that would end Pennsylvania's status as the only state without a complete budget, has provoked strong opposition, but advocates for the arts likely face an uphill climb in their effort to derail it.

The proposed elimination of the current exemptions for artistic and cultural events is expected to generate roughly $120 million a year — about twice as much as those activities currently receive through various state appropriations, Corman said.

A portion of the revenue would be funneled into a special fund reserved for supporting the arts and cultural institutions. The rest would help pay for other items in the nearly $28 billion state budget deal struck by Gov. Ed Rendell and leaders of three of the four legislative caucuses.

The percentage that would be earmarked for the special fund was still being firmed up — like many details of the budget deal — and could generate more or less than previous appropriations for artistic and cultural events, Corman said.

"It's up in the air because it hasn't been written," Corman said in a telephone interview from his district office in Bellefonte.

The idea surfaced for the first time Friday night, shortly before the governor, Corman and other top lawmakers announced the budget deal could end an impasse nearly three months into the new fiscal year.

The partisan deadlock forced tens of thousands of state employees to temporarily work without pay until Rendell signed a partial budget in August providing limited funds to keep state government operating. But some day care centers have closed, some preschools have not yet opened and mentally ill people have to wait longer for counseling because hundreds of nonprofit agencies have not received state reimbursements on which they rely.

The money to be generated from extending the 6 percent tax to artistic and cultural events was a final component to seal an agreement between Senate Republicans and Rendell, who had demanded more reliable sources of revenue before he would sign on.

Advocates for arts groups said they were stunned by news of the proposal and said it would discourage people from attending performances or visiting cultural institutions.

"What were you thinking?" asked Peggy Amsterdam, head of the Philadelphia Cultural Alliance at a Monday night meeting where hundreds of arts leaders criticized the budget negotiators and vowed to try to block the proposal.

"It will price everyday people out of arts experiences and it will push key cultural institutions to the brink," Amsterdam told the gathering at the Annenberg Center for the Performing Arts.

On the other side of the state, the executive director of the Pittsburgh Ballet Theatre expressed a similar sentiment.

"It's a bad idea to tax the nonprofit arts sector," said Harris Ferris.

Philip Horn, executive director of the Pennsylvania Council on the Arts, which dispensed $14.5 million in state grants to nonprofit arts and cultural organizations last year, said he did not learn about the proposal until Saturday.