The Rockville City Council on Monday adopted a $28.2 million operating budget for next year that keeps the city's property tax rate at 88 cents per $100 of assessed value.

However, because of higher assessments and charges for city services, the owner of a $105,000 house -- the city's current average -- will pay $27.60 more next year, city officials said.

A slightly lower average was cited when the budget was first proposed but has since been recalculated to reflect 5 percent increases in assessments over last year.

Of the $27.60 increase, $19.80 is from higher property assessments and $7.80 reflects higher charges for refuse collection, officials said.

The increase in the budget, which is about 7 percent higher than last year's spending plan, will be funded mostly through additional property tax revenue, which will total $9.6 million, officials said.

The City Council also approved a $36 million, six-year capital improvements budget.

Of the $36 million, $15.8 million will be spent on transportation projects, $1.4 million on health and safety projects, $1 million on the town center and the remaining $2.8 million on recreation projects.

Project funds include $50,000 for construction of a catwalk at the F. Scott Fitzgerald Theatre, $9,000 for the purchase of land adjacent to the Beall Dawson property and $30,000 for sediment removal for the Ritchie Parkway area. Washington Grove Election

Voters in Washington Grove elected a new mayor and three Town Council members at last weekend's town elections.

Former council member Charles Challstrom ran unopposed for the one-year mayoral post, getting 112 votes. He replaces Barbara S. Hawk, who served two terms.

Among council members, incumbent Carol Uhlendorf won reelection with 85 votes. Donald Henniner won his first council seat with 67 votes. Donald Gallagher was elected unopposed to a one-year term on the six-member council with 114 votes.

More than a third of the registered voters in Washington Grove cast ballots, election officials said. Takoma Park Street Festival

Nearly 14,000 people turned out to dance in the streets, sample exotic foods and listen to a variety of musicians during the city's annual Old Town Street Festival Sunday. City police said it was one of the largest crowds the event has drawn in recent years.

The day-long festival was held near the Gazebo on Carroll Avenue. Revelers were treated to music ranging from rock 'n' roll to Irish-American folksongs, as well as demonstrations of breakdancing, karate and crafts. Coming Up:

*Barnesville Town Commission, 8 p.m. Monday, 17925 Barnesville Rd.

*Gaithersburg City Council, 7:30 p.m. Monday, City Hall, 31 S. Summit Ave.

*Poolesville Town Commission, 8 p.m. Monday, Town Hall, Elgin Road and Fisher Avenue.