The citizens group that sponsored Prince George's County's tax-limiting TRIM charter amendment filed suit yesterday against the State of Maryland in an effort to raise taxes for owners of apartments and commercial properties.

The TRIM group, represented by Montgomery County state Del. David Scull, charged in a suit filed in Anne Arundel County Circuit Court that the state consistently undervalues commercial and industrial property for tax purposes.

As a result, the suit charges, the state unfairly discriminates against taxpayers who own single-family homes and condominiums.

Although the 19 plaintiffs are residents of various parts of Maryland, the suit most directly addresses the tax problems of homeowners in Prince George's, where the voter-approved TRIM amendment limits the total amount of property taxes that can be collected in any year to $142 million.

If the assessments -- and taxes -- of commercial and apartment properties in Prince George's were raised under a new system of calculation, as the suit asks, the taxes of homeowners would go down because of the freeze on total collections.

The TRIM group argues that apartments and some warehouses, office buildings and marinas should be assessed at the value thay would have if they were sold as condomnium units.

Apartment values now often are calculated by tax assessors on the basis of estimated of the income they produce for owners.