HARRISBURG — In the campaign to elect Pennsylvania's 46th governor, Tom Corbett casts a long shadow.

The buttoned-down, white-haired state attorney general is the best-known of the six candidates, due mainly to his office's conviction-winning corruption probe of the Legislature.

Corbett is endorsed by the state GOP, and independent polling suggests he is likely to be the Republican nominee despite opposition from Rep. Sam Rohrer, one of the Legislature's leading conservatives.

The prospective Democratic nominees, meanwhile, are struggling to become household names and set themselves apart in a crowded field barely six weeks before the May 18 primary:

• Allegheny County Executive Dan Onorato, whose $6.5 million campaign war chest as of Dec. 31 made him by far the best-financed candidate in either party, bills himself as the only one with experience as a government chief executive.

• Montgomery County Commissioner Joe Hoeffel, a former congressman and state legislator from suburban Philadelphia, is the political "progressive" with the most liberal philosophy.

• State Auditor General Jack Wagner, a former state senator from Pittsburgh, promises to crack down on the kind of waste and fraud that his audits of state agencies have suggested.

• State Sen. Anthony Hardy Williams of Philadelphia, the only legislator in the Democratic primary, advocates a significant expansion of taxpayer-financed alternatives to public schools through his "school choice" agenda.

Gov. Ed Rendell's second term ends in January. The state constitution bars the Democrat from seeking a third consecutive term.

The campaign to choose Rendell's successor is unfolding amid challenging times for state government.

The national recession has pushed statewide unemployment to its highest rate in 25 years. Meanwhile, billions of federal economic stimulus money that is helping prop up this year's state budget is set to disappear and a multibillion-dollar increase in taxpayers' annual contribution to state and local public pension funds is expected to come due early in the next administration.

Taxes, spending and job creation are on the lips of all the candidates.

But most of the Democratic would-be governors also are fixated on reforming state government — especially the legislative branch which Corbett has targeted — and tamping down the partisan rancor that has prevented a single state budget from being passed on time since Rendell took office in 2003.

Wagner advocates convening the state's first constitutional convention since 1968 to overhaul the legal foundation of state government.

Onorato would withhold a day's pay from the governor and members of the Legislature for every day the state goes without a budget after the June 30 deadline.

Hoeffel would establish a nonpartisan Legislative Budget Office to provide objective estimates of program costs and minimize partisan disputes that can paralyze the General Assembly.

"I've never seen a time in my life where the public is so ready to reform Harrisburg," Onorato said during a recent get-acquainted walking tour of the Philadelphia neighborhood where his campaign office is located.

If Pennsylvania voters are in the mood for reform, Corbett helped put them there.

The probe of state lawmakers' illegal use of taxpayer resources for political campaigns — activity that a newspaper brought to light in early 2007, while voters were still fuming over the Legislature's dark-of-night pay grab two years earlier — has consumed most of Corbett's five-year tenure as Pennsylvania's chief legal officer.

Twenty-five current or former legislators and staffers — 15 Democrats and 10 Republicans — have been charged so far in the ongoing investigation. Of the dozen cases decided so far, 10 have resulted in criminal convictions or guilty pleas.

Corbett, 60, insists he did not seriously contemplate running for governor until after his re-election in 2008, but he is living proof that good government can be good politics. A Quinnipiac University poll in early March showed the suburban Pittsburgh resident with an 8-1 edge over Rohrer among the roughly half of GOP voters who had made up their minds.

"I am doing my duty," Corbett said in an interview during a campaign visit to a Lancaster job-training center. "We've put a great deal of effort in this because I think this is so important to the body politic and to the people of Pennsylvania."

Rohrer, 54, who has represented his Berks County legislative district for 17 years, bills himself as the "authentic conservative" in the GOP race but recognizes he is playing David to Corbett's Goliath.

When the Republican State Committee met at a Harrisburg hotel to endorse candidates in February, Rohrer demonstrated his flair for showmanship by staging a daylong Mobilize for Liberty counter-convention down the hall that drew 250 people.

The centerpiece of Rohrer's campaign is his long-standing plan to replace school property taxes by extending the state sales tax to more transactions and turn over responsibility for funding public education to the state.

Corbett and Rohrer have both signed written pledges to oppose any tax increase as governor.

The Democratic contest defies easy analysis, with one pair of candidates from southwestern Pennsylvania and another pair from the southeast potentially splitting the vote in their home regions while all four strive to elevate their statewide name recognition. The Quinnipiac poll showed none of them had attracted even 20 percent support.Onorato, who last week began airing the first TV commercials of the campaign, touts his success as Allegheny County's top elected official in shrinking a bloated bureaucracy, cutting property taxes and turning around the local economy as proof of his executive talent.The youngest candidate at 49, Onorato offers a comprehensive plan for governing, including more than a half-dozen position papers spelling out his initiatives in areas that include education, economic development, public safety, agriculture and government reform.He plays down his approval of an unpopular 2-year-old tax on alcoholic drinks to help finance public transit in his county, saying the Legislature allowed no other alternative to increasing property taxes, which he opposed."The drink tax shows you everything that's wrong with Harrisburg," he said. " If anybody tries to attack me on this, I'm all ready for it."Onorato is backed by some of Rendell's key supporters — former Rendell chief of staff John Estey is a friend and former University of Pittsburgh Law School classmate — and shares the incumbent's views on many issues. But he chafes at comparisons between the incumbent, who has not publicly taken sides in the primary, and himself.Hoeffel, 59, a fixture in Pennsylvania politics for more than three decades, pledges that his administration would promote "values that are socially liberal and programs that are fiscally responsible."In a plan that rivals the breadth of Onorato's, Hoeffel advocates shifting more of the local property-tax burden onto income taxes and replacing Pennsylvania's flat-rate income tax — one of only a handful nationally — with a "graduated" income tax like the federal system that imposes the highest rates on the wealthiest taxpayers.To pay for modernizing Pennsylvania's highways and public transit systems, he proposes doubling transportation funding — partly through increases in the gasoline tax and higher registration fees for vehicles beyond a household's first vehicle.He also advocates legalizing same-sex marriages and outlawing discrimination based on sexual orientation or gender identity.Wagner, 62, came closer than Onorato to winning the Democratic State Committee endorsement in February but fell short of the needed two-thirds majority. He is running on his record as the state government's elected fiscal watchdog.Based on questions raised by some of the 5,000 audits a year his office performs, Wagner has publicly accused the Rendell administration of mismanaging tasks as diverse as awarding multimillion-dollar state contracts, conducting dam-safety inspections and determining eligibility for Medicaid payments.Wagner promises to cut wasteful spending and seek additional federal money to finance initiatives that include free tuition at state-owned universities for top students and expanded infrastructure improvements.A Marine veteran who was awarded the Purple Heart for wounds he suffered in the Vietnam War, Wagner said his present job qualifies him as a government outsider even though he's been an elected official for more than a quarter-century.Williams, 53, who declared his candidacy only in February, is counting on strong support from Philadelphia's large, mostly Democratic, African-American community. He's been endorsed by black leaders including Mayor Michael Nutter."School choice" is an umbrella term for policies that allow parents to send their children to private or specialized schools at taxpayers' expense, and it has generally been a Republican issue. But Williams' background — he received his high-school education at the Quaker-run Westtown School in Chester County — helps explain his advocacy of the concept.