The Philadelphia delegation in the state House of Representatives plans to unveil a package of four bills Tuesday that would give the city new authority to assess, collect and provide relief from property taxes.

The bills are designed to ease the city's anticipated switch this spring to a new property tax system based on the market value of property.

The new system - billed as a measurably fair replacement for one rife with inaccurate data and prone to political manipulation - will nonetheless have a seismic impact on the tax landscape.

Among the side effects of Mayor Nutter's Actual Value Initiative (AVI) is a shifting of the tax burden from commercial properties to residential homes, and stiff increases for people living in historically low-tax areas - such as Northern Liberties or Graduate Hospital - where home prices have spiked.

The four bills, taken collectively, are meant "to lessen the negative impact this could have on real Philadelphians," said Rep. Cherelle L. Parker, chair of the city's 28-member House delegation.

The bills include:

A measure to authorize the city to place liens on all property that landlords own, if they are delinquent on taxes. Nearly 100,000 parcels - about 1 in 6 - are tax delinquent, Parker said. The city's inability to collect this money has been a sore spot in the AVI debate. If more of that money could be collected, the tax rate could drop across the city.

A measure to allow tax relief to longtime residents in gentrifying neighborhoods based on income and age, something permissible now only in Allegheny County, which includes Pittsburgh. Without so-called "means testing," relief to longtime residents in neighborhoods like Northern Liberties would undoubtedly extend to unintended, wealthier residents. That loophole has been an argument against such relief.

Seek a Constitutional amendment authorizing the city to tax commercial and residential property at different rates. Many cities in the Northeast tax commercial buildings at a higher rate, but Pennsylvania's "uniformity clause" prevents that here. A Constitutional amendment must pass the General Assembly for two consecutive years before being put to voters - making this a years-long proposal.

Give the city the ability to let some homeowners pay their property tax bills in installments. Because 40 percent of Philadelphia homeowners do not have mortgages - and don't pay monthly into an escrow account for their taxes - they have to pay the full amount at once.

The bills are sponsored by Parker and Reps. Michael O'Brien, Michelle Brownlee and Michael McGeehan. Parker said she hoped every member would cosponsor each of the bills before they are introduced next week.

"We're shooting for unity," she said. "It's very important that our delegations are unified."

Parker, a Democrat, called the package a work of "unprecedented" cooperation of city politicians in the House, Senate and City Council.

The proposals first were aired this fall in a joint letter, signed by Mayor Nutter, Council President Darrell L. Clarke and School Reform Commission Chairman Pedro Ramos.

At that time, Parker had asked the three to sign the letter in another show of unity, as the General Assembly was debating passage of a bill key to implementing Nutter's property tax plan.

Nutter spokesman Mark McDonald said the administration remained behind the proposals. Clarke echoed that support.

"We've been saying all along we need every tool imaginable," he said. "It's better to have them and not need them."

Contact staff writer Troy Graham at 215-854-2730 or tgraham@phillynews.com, or follow on Twitter @troyjgraham.