NEW YORK (CNNMoney.com) -- Housing prices have plummeted, but property tax bills probably won't budge.

This January, local tax authorities will begin to send out property assessments for 2009, telling homeowners what their property is valued at, and how much their tax bill is.

But many assessments won't reflect any of the steep home price declines that have been making headlines for the last year or so.

And even if property assessments do drop, property tax bills won't necessarily be any lower.

"I think you're going to see a lot more taxpayer protest this year," said Bruce Hahn, president of the American Homeowners foundation, a non-partisan consumer advocacy group.

A huge runup slows

Property taxes climbed relentlessly earlier this decade as home prices rose, according to Pete Sepp, spokesman for the National Taxpayers Union. This year Americans will pay more than $400 billion in property taxes, up about 25% from levels in 2004 and double what they paid ten years ago.

At best, says Sepp, those steep increases may start to level off.

Nevertheless, homeowners are already pressing assessors for lower tax assessments.

"For my first 25 years [as an assessor], nobody ever asked me to lower the assessment based on a home selling for less down the street. There are many such inquiries this year," said Ken Wilkinson, the tax assessor for Lee County Fla., which includes Cape Coral and Ft. Myers.

He estimates that 80% of county residents have seen the value of their homes decline. The median price of existing homes fell more than 25% in the 12 months ending June 30, according to the Housing Opportunity Index compiled by Wells Fargo (WFC, Fortune 500) for the National Association of Home Builders.

Home prices in Moreno Valley, Calif. a city of 187,000, have fallen by more than a third over the past two years, according to the same index. And that has many more homeowners clamoring for reassessments, according to Barry Foster, the city's economic development director.

But even if local prices are way down, taxpayers may not win a lower assessment, because there can be a big lag time between when the home sales used to calculate them take place and when the assessment is actually issued.

To calculate 2009 assessments, for example, assessors will use home sale prices from 2008 or even earlier, according to Sepp. Usually this works to taxpayers's advantage, since price increases take a while before they are fully reflected in assessments.

That's why it's typical for most homes to be under-valued, according to Bruce Hahn of the American Homeowners foundation. But that's also why many homeowners aren't likely to see their assessments shrink immediately.

Lower values, same bill

There's another reason why homeowners are unlikely to see any decrease in property tax bills. In some states, such as California, Washington State, Massachusetts and Idaho, taxes are based on the last resale price of the house. Even a home worth $500,000 in California may be taxed based on the sale price when it was bought 10 years earlier for $200,000.

"Because the assessment is based on acquisition value, it's difficult to get that re-evaluated," said Sepp.

That's why the market value of most homes in these states exceeds the assessed tax values. The owners with best case for a reassessment are the ones who bought at the top of the market and have seen their values drop by a third or more, like many of Moreno Valley's residents.

Even if citizens do receive a lower assessment - and this year Wilkinson expects to lower assessments for most taxpayers in Lee county, Fla., by 20% or more - their property tax bill may not shrink at all.

Tax collectors often raise tax rates to offset lower assessments to meet their budgets, which will be very strained this year. Assessments go down but rates go up so that the tax collections stay roughly the same.

"State and local governments depend very heavily on real estate taxes and they are reeling from a loss of revenues from sales taxes and other sources," said Bruce Hahn.

Once homeowners get their bills, they'll have several weeks to contest their assessments, according to Hahn.

He suggested they go online to real estate evaluation sites such as Zillow.com to determine how far property values have fallen in their communities. They can also cite comparable home sales for similar properties to make their cases.

"Some tax assessors have been very reasonable," said Hahn, "but others are under great pressure to keep revenues up."