The study, which Beaufort County Council members have said they wanted for nearly two years while debating the 15 percent cap, suggests income-based tax exemptions as a better approach to tax relief than an across-the-board cap.

Such exemptions are not allowed under state law, however.

The cap, which is allowed, would hold increases to 15 percent when property values are updated every five years on the county's tax rolls, as required by the state.

For example, a $100,000 home that increased in value to $200,000 would be taxed at only $115,000.

County Council in 2003 delayed for one year the scheduled five-year reassessment of property values to gather more information on the cap, which some members want to adopt.

But the council is running out of time to make a decision this year. County staff members have said they need to know by April 1 whether to process tax bills with or without the cap.

Council members have said the Clemson study would show the cap's effects locally and play a large role in their decision. The study, which officials received Monday, uses property tax information from 1997 and 1998, the years before and after the last reassessment.

Without a cap on rising property tax values, some longtime landowners and owners of expensive waterfront properties will continue to see significant increases in property tax bills as property values climb, the study states.

But the tax cap merely shifts the tax burden to taxpayers whose property is not rising in value as quickly.

"Capped reassessment would help stabilize the tax bills of these owners, but it would do so at the expense of other taxpayers in the county," according to the study, written by Ellen Saltzman, research associate for Clemson University's Strom Thurmond Institute of Government and Public Affairs.

Councilman Mark Generales, chairman of the Finance Committee and a cap supporter, declined to comment on the study Tuesday because he had not yet read it.

"I'll have to see if it's what we were asking for or if they decided to opine all over the place, which is not what we asked for," Generales said. "We just asked for some number crunching."

He said the county wanted an analysis of how property sales would affect the overall tax system under the cap. Properties sold now are taxed at the last assessed value until the next scheduled five-year reassessment. But the cap would change that, taxing properties instead at market value when they are sold.

Saltzman said she was not asked for such a specific analysis. Instead, she was asked whether the cap would affect all property owners equally and what other information Beaufort County should consider.

"I picked what I thought was important," Saltzman said. "I really did try to provide a thorough but objective analysis."

She said her study presents the pros and cons but leaves a value judgment to the council.

The study lists two benefits of the cap: It would bring tax relief to owners of property rapidly increasing in value, and it would make taxes more predictable in areas where property values are rising quickly, encouraging development there.

But both of those benefits, viewed from a different perspective, are among five drawbacks of the cap outlined in the study.

Savings for owners of property rising quickly in value can be a drawback because those savings are subsidized by taxpayers whose property value is not rising as much.

Encouraging development in areas where property values are rising can be a drawback because generally those are the areas where development already is happening, Saltzman said. And increased development usually means a higher demand on public services.

"You're putting a lot of pressure on places that might have some environmental and transportation issues," she said.

"Counties do not need development incentives for desirable land; they need them for undesirable land," she wrote in the study.

The cap also would stifle real estate sales because once a property is sold, the cap is removed and the new owner pays taxes initially at market value. The cap is then reapplied to the higher value.

"Owners of property that is rapidly increasing in value will be more likely to hold onto their property than sell it," Saltzman wrote.

Depressed real estate sales would reduce revenues collected by the Town of Hilton Head Island's 0.25 percent real estate transfer fee, used to preserve open space.

Another drawback is the cap benefits commercial and rental property more than owner-occupied homes. That increased savings comes because commercial and rental properties are taxed at 6 percent of their value, while owner-occupied homes are taxed at 4 percent.

But without the cap, commercial and rental property owners can pass along higher tax burdens to tenants, while homeowners do not have that option.

A final drawback is that state laws allowing the cap do not allow counties to recoup any of the dollars lost under it when a property is sold. Developers of agricultural land, by contrast, must pay five years of taxes at the new designation when they develop the land.

Saltzman said a price for the study has not yet been negotiated with the county, but she estimated it would be less than $5,000.

An opponent of the cap, Councilman Frank Brafman, said he thought the study validated the arguments against adopting it, although it could have explored further the effect on the real estate industry.

"That's what I thought it would be, opinion, based on fact," he said. "I think there are enough facts in there to justify the opinions."