Prince George's County officials said yesterday that the county's TRIM charter amendment, which was billed to voters as a way to reduce property taxes, will not lower the property tax bills of most homeowners in the county this year or for many years to come.

The amendment, which puts a ceiling of about $140 million on total property tax collections in future years, was designed to help spread the property tax burden -- giving homeowners more and more relief as new development moves into the county.

However, after studying the patterns of growth of the county's tax base, county officials now say that even with new construction, the bills of most county homeowners will rise next year unless new tax-cutting measures are approved by the new county council and incoming county executive Lawrence J. Hogan.

The real beneficiaries of the program, county officials say, will be owners of stores, factories, warehouses and apartments, whose taxes will, in most cases, drop every year.

County finance director William Brown said yesterday that it is unlikely that most homeowners will have their tax bills lowered strictly because of TRIM for "many, many years... probably close to 10 years."

David Bird, one of the two authors of TRIM who was elected to the Maryland House of Delegates after campaigning for the charter amendment, said yesterday he was "not convinced" by the analysis of Brown and county tax officials.

"No one ever brought up this possibility before," Bird said. "I'll have to look at it."

But Sam Wynkoop, who advised outgoing County Executive Winfield M. Kelly Jr. before Kelly endorsed TRIM, agreed that many who voted for TRIM might have been misled.

"This was not Kelly's proposal," Wynkoop said. "We endorsed it because it was looked on as a popular movement to limit government."

According to Harry S. Shipp Jr., the chief of the county's tax assessment division, new development and higher assessments of existing homes and businesses will increase the county's property tax base by about 8 percent this year.

That rise in the value of taxable property will force the county, under TRIM, to cut the county's tax rate by a corresponding 8 percent, from the current $3.31 to $3.06, according to finance department officials.

Nevertheless, the average rise in the assessment of county residential property will be between 9 and 10 percent, Shipp said. Thus, Shipp said, most homeowners will have to make up the difference between the drop in the tax rate and the rise in their assessements due to inflation. The avrage increase will be 2 percent, but many homeowners will have bills as much as 7 percent higher.

During the election campaign, Kelly repeatedly said that it would be necessary to obtain legislative approval of a "tier tax" system -- under which residential and commercial property is taxed at different rates -- in order for homeowners to fully benefit from TRIM.

Both Kelly and Hogan supported TRIM as a popular movement that the county could accept financially by making some budget cuts. But neither focused on what the actual effects of TRIM might be to taxpayers.

What causes the discrepancy, Shipp said, is that the value of commercial property in the county is rising at a much slower rate than that of residential property. For that reason, the growth of the county's assessable base lags behind the growth in most homeowners' assessments.

The discrepancy in the rate of inflation for commercial and residential properties is likely to keep homeowner taxes rising -- and commercial and apartment taxes dropping -- for many years to come, Brown said. New development will have a negligible impact on this trend for at least five years, contrary to the belief of TRIM's authors, Brown added.