Concerned with their residents' growing tax bills, officials in Rockville and Gaithersburg adopted their fiscal 1991 budgets holding the line on property taxes while Takoma Park dropped its tax rate by more than 5 cents.

In Rockville, which can boast of an expanding tax base, Mayor Douglas M. Duncan and the City Council on Monday approved a $47.4 million operating budget, a package that maintains the current property tax rate while raising fees for trash pickup and water and sewer use. The budget represents an increase of $2 million over current spending.

Despite a bid by Duncan to cut the property tax rate by 1 cent, the council favored holding the tax rate to 83 cents per $100 of assessed value. Garbage collection fees will increase 6 percent to $20.30 a year, the water rate will jump 7.6 percent to $1.13 per thousand gallons, and the sewer rate will rise 6 percent to $2.40 per thousand gallons. Duncan has said that those increases are intended to cover the additional costs caused by new federal regulations and higher fees charged to the city by Montgomery County to dump trash at the county transfer station.

The mayor and council also approved a $67.6 million six-year capital improvements program, of which $31 million is earmarked for transportation and road projects.

The tax rate also will remain stable in Gaithersburg, where Mayor W. Edward Bohrer and the City Council on June 4 adopted a $16.5 million combined operating and capital budget, an increase of 27 percent over the budget approved last year. The tax rate remains 53 cents per $100 assessed value.

This marks the 26th straight year without a tax rate increase in rapidly-growing Gaithersburg. Still, as in other Montgomery County communities, residents can expect higher property tax bills because of rising assessments.

The $5.3 million capital spending plan includes $950,000 for a proposed senior citizens center and $1.5 million toward recreational facilities at the city's Summit Hall Farm Park on Route 355.

In Takoma Park, where city officials have spent the budget season determined to provide their constituents with some tax relief, the City Council voted Monday to lower the property tax rate by 5.5 cents in the $8.2 million budget. The council paid for that dropoff in revenue by taking $580,000 out of the reserve fund.

Although the new tax rate of $1.77 per $100 assessed valuation should soften the blow for homeowners, they can still expect higher tax bills because of climbing property assessments. Assistant City Administrator Beverly K. Habada said that with the maximum 15 percent assessment increase allowed by the state, the owner of a $100,000 house in Takoma Park who now pays $786 in property taxes would pay $877 beginning July 1.