HARRISBURG — It’s budget season again for Gov. Tom Corbett, and that means the same thing as last year: His approval rating has plummeted as Pennsylvania’s no-new-taxes chief executive preaches austerity for public schools and social services while prescribing tax cuts and tax breaks for businesses.

This year, though, the stakes are higher. Elections are in the fall, and the solid GOP majorities Corbett has enjoyed in both legislative chambers are at risk of narrowing – with Democrats planning on using the Republican governor as a foil.

In addition, Corbett is asking the Legislature to fulfill what could be his biggest request yet: A $1.7 billion, 25-year tax credit for petrochemical refiners such as the Netherlands-based oil and gas giant Royal Dutch Shell PLC, which pocketed a tidy $7.3 billion profit in just the first three months of 2012.

It would be the state’s largest-ever financial incentive package – corporate welfare, critics say – and it is shaping up as perhaps the biggest test of Corbett’s ability to persuade lawmakers and the public, especially since lawmakers typically like to avoid divisive battles close to an election.

Political capital would help, but Corbett doesn’t have much to spend.

The Connecticut-based Quinnipiac University released a poll June 12 that showed Corbett’s approval rating sank to 36 percent – the lowest of his 18-month tenure and practically the kiss of death for anyone seeking re-election. That nearly echoed the 39 percent he scored in a Quinnipiac poll during budget talks a year ago, except that the proportion of disapproving votes widened from 38 percent then to 47 percent now.

Meanwhile, lawmakers roundly point to what they view as Corbett’s mystifying detachment: They expect him, as they have with previous governors, to mount a town-to-town and, in the statehouse, office-to-office campaign to drum up support for his agenda.

But he doesn’t.

Republicans also winced when he didn’t announce his proposal for the petrochemical tax credit – Pennsylvanians first heard about it in news reports and Corbett had little ability to sway the initial coverage and editorials. The liberal Pittsburgh City Paper produced a cover that showed Corbett and a briefcase-toting man in a business suit in a send-up of Time Magazine’s splashy May 21 breastfeeding cover. A Philadelphia Daily News front page screamed, “SHELL SHOCK.”

In many parts of the state, Democrats fully intend on using Corbett as their punching bag in fall campaigns.

“Many of the Republicans running, they all say they’re going to represent their local constituents,” said Sen. Daylin Leach, the Montgomery County Democrat who chairs the Senate Democratic Campaign Committee. “But if you look at their votes, we see party-line votes where people who run as moderates vote for the craziest stuff once they get up here. If you say your Republican opponent is going to be a rubber stamp for Corbett, odds are that it’s true.”

Only Republicans voted for Corbett’s first budget – which slashed more than $1 billion in aid for public schools and 18 state-supported universities. Just six Democrats voted for the Republican-penned Marcellus Shale law in what many Democrats viewed as an industry giveaway by Corbett, and none raised a hand for the voter identification law, now one of the nation’s toughest. Both are being challenged in court.

Democrats will connect the Shell tax credit to Republican-sponsored cuts in aid to education, people with disabilities and health and human services that they say are driving layoffs and increases in local property taxes.

“We’ve already given away the store to the Marcellus Shale industry and now we’re proposing to give away billions of tax dollars?” said Luzerne County Rep. Phyllis Mundy, the ranking Democrat on the House Finance Committee.

For his part, Corbett has been through ups and downs in his approval rating before.

“If you’re going to do this job, you can’t be looking at that,” he told a radio interviewer Wednesday. “The one thing I learned last year, if you looked at the numbers, they were bad during the course of the budget last year. They got better as people see things other than the budget issues.”

By late September, his approval rating hit 50 percent, Quinnipiac reported, and stayed in the high 40s through November. Republican lawmakers are privately urging Corbett to make a strong public case for the tax credit – it is designed to lure an entire petrochemical industry to a state that has bled 40 percent of its manufacturing jobs since 1990. It also helps that labor unions aligned with Democrats are supportive.

But Republicans also remember complaining about efforts by Corbett’s predecessor, Democrat Ed Rendell, to help Comcast Corp. get a headquarters skyscraper in Philadelphia or introduce a tax credit that benefits filmmakers that use the state as a backdrop.

“I don’t know many of my colleagues that are scared of this issue” in the fall election, said

Rep. Rob Kauffman, R-Franklin. “It’s just a matter of, we want to do things right. This is a difficult issue. Although we want to support our governor, this is not something that many of us would have supported in the past.”

Meanwhile, Republican legislative leaders are pressing Corbett to accept a budget for the fiscal year beginning July 1 that would undo his second straight year of proposing cuts to public schools and universities, if not to social services and aid for the poor. Still, nothing Republicans are proposing seems likely to stop thousands of layoffs by school districts.

Senate President Pro Tempore Joe Scarnati,

R-Jefferson, said Corbett is poised to score victories for his agenda this month – including sealing the tax-credit deal for Shell – and he expressed confidence that the Quinnipiac’s polling reflects the temporary fishbowl of budget negotiations.

Besides, he said, the fall election will be more about the men at the top of the ticket – President Barack Obama and Mitt Romney.

“The presidential race just overshadows everything,” Scarnati said. “All this debate, everything we’re talking about now, come September and October, we’re going to be hearing about who supports Romney and who supports Obama.”