Tax assessments on single-family homes in the District of Columbia increased 18.6 percent in the past year, bringing the taxable value of an average home to $59,959, the D.C. Department of Finance and Revenue reported yesterday.

The department said the average annual tax bill for a city homeowner is expected to rise by $51 to a citywide average of $652. Notices of the new assessments will be mailed to homeowners today, and the bills will be due in two installments next September and March.

In one neighborhood -- Massachusetts Avenue Heights, which includes the Embassy Row area west of Rock Creek Park -- the average assessment was $210,925, the first time in city history, that the average assessment for a neighborhood has exceeded $200,000. That pushed the estimated average tax bill up $219 to a total of $2,746.

On Capitol Hill, where the rate of increase was only about half of the citywide average, the typical taxpayer can expect his tax bill to go down by $6, to $897. But Donald B. Beach, the chief city assessor, speculated that the rate there will rise next year, fueled by the rising cost of house sales.

This 18.6 percent increase in citywide assessments is slightly below the 19.7 percent reported last year and far less than the 32 percent rise reported in 1976 and 42 percent in 1977.

Although the law calls for assessing property at its full market value, the new assessments in most neighborhoods remain far below the current sales values of the homes. Beach explained that the new assessments are based upon sales transactions and property inspections in 1977, the last year for which full data is available.

In 1978, according to figures released last week, the average sales value of homes in Massachusetts Avenue Heights, for example, topped $350,000. Median sales prices in 28 of the 56 assessment neighborhoods went above $100,000 last year, compared with only 10 in 1976.

The finance department said the total taxable value of all private property in the city reached close to $12.4 billion, a rise from $10.7 billion last year.

Of that, about half -- $6.5 billion -- represented the value of 122,500 single-family homes. Of the balance, $1.56 billion was the value of apartment houses and $4.37 billion was commercial property.

Real estate taxes in the District, yield about $195 million a year, exceeded as a source of city revenue only by the personal income tax, which totals more than $250 million.

The tax bills are expected to rise more slowly than the new assessments because a city law limits the total increase in property tax collections to 7 percent a year.

The finance department reported to Mayor Marion Barry that collections would reach that level if the residential tax rate is set at $1.36 for each $100 of assessed value. The residential tax rate this year is $1.54 for each $100. The tax rate on business property is $1.83 for each $100.

The actual levels are recommended by the mayor and adopted by the council.

The amounts of tax increases or reductions are expected to vary from neighborhood to neighborhood because the assessed values are rising faster in some areas than others, Beach said.

Values in Columbia Heights -- an area along 14th Street and Georgia Avenue NW north of Florida Avenue, including the Cardozo area -- rose by 36.1 percent last year, the highest rate in the city. The average valuation reached $27,211, and the taxes will rise $102 on each home, to $384.

Values in adjacent 16th Street Heights, northward from Upshur Street, rose by 7.2 percent, the lowest rate for a major city neighborhood. There the average valuation reached $48,920, and the taxes are expected to decline by $21, to $543.

Rod DeBozy, a supervising assessor, said Columbia Heights increased in value faster because of a large number of row houses being renovated by recent buyers. "It is like Mount Pleasant five years ago," he said.

The tax assessments on all owneroccupied homes can be reduced by a $9,000 homeowner's exemption. The finance department said it will mail affidavit forms soon for homeowners to claim these exemptions.

The finance department said business property in the downtown area increased in value by 12.5 percent.

Taxpayers may appeal new assessments to an independent body called the Board of Equalization and Review. Appeal forms which must be filed by April 15, are available in Room 202 of the District Building, Room 2000 of the Municipal Center Building or at any public library. New D.C. Average Residential Assessment (TABLE) Neighborhood(COLUMN)New Average(COLUMN)Percent(COLUMN) (COLUMN)Single Family(COLUMN)Increase in(COLUMN)New Average Name(COLUMN)Assessment(COLUMN)Assessments(COLUMN)Tax Levy American University Park(COLUMN)$ 85,958(COLUMN)21.5(COLUMN)$1,047 Anacostia(COLUMN)29,100(COLUMN)27.9(COLUMN)273 Barry Farms(COLUMN)29,134(COLUMN)27.0(COLUMN)274 Berkley (Upper Foxhall)(COLUMN)175,158(COLUMN)22.3(COLUMN)2,260 Brentwood(COLUMN)32,148(COLUMN)17.2(COLUMN)315 Brightwood(COLUMN)49,937(COLUMN)22.4(COLUMN)556 Brookland(COLUMN)40,238(COLUMN)17.2(COLUMN)425 Burleith(COLUMN)94,192(COLUMN)22.1(COLUMN)1,159 Capitol Hill(COLUMN)74,941(COLUMN)10.8(COLUMN)897 Central (Downtown)(COLUMN)71,576(COLUMN)23.0(COLUMN)851 Chevy Chase, D.C.(COLUMN)93,474(COLUMN)13.9(COLUMN)1,149 Chillurn(COLUMN)49,313(COLUMN)21.5(COLUMN)548 Cleveland Park(COLUMN)110,650(COLUMN)18.9(COLUMN)1,382 Colonial Village(COLUMN)117,511(COLUMN)16.5(COLUMN)1,476 Columbia Heights(COLUMN)37,211(COLUMN)36.1(COLUMN)384 Congress Heights(COLUMN)33,508(COLUMN)12.0(COLUMN)333 Crestwood(COLUMN)94,760(COLUMN)23.0(COLUMN)1,166 Deanwood(COLUMN)30,707(COLUMN)21.3(COLUMN)295 Eckington(COLUMN)29,924(COLUMN)16.4(COLUMN)285 Foggy Bottom(COLUMN)95,940(COLUMN)20.4(COLUMN)1,182 Forest Hills(COLUMN)127,218(COLUMN)24.7(COLUMN)1,608 Fort Dupont Park(COLUMN)39,285(COLUMN)21.1(COLUMN)412 Foxhall(COLUMN)93,868(COLUMN)21.0(COLUMN)1,154 Garfield (Conn. Ave.)(COLUMN)80,315(COLUMN)20.7(COLUMN)970 Georgetown(COLUMN)152,187(COLUMN)29.9(COLUMN)1,947 Glover Park(COLUMN)82,182(COLUMN)22.1(COLUMN)995 Hawthorne(COLUMN)109,155(COLUMN)12.0(COLUMN)1,362 Hillcrest(COLUMN)41,382(COLUMN)16.2(COLUMN)440 Kalorama(COLUMN)122,332(COLUMN)22.8(COLUMN)1,541 Kent(COLUMN)135,817(COLUMN)15.4(COLUMN)1,725 LeDroit Park(COLUMN)30,809(COLUMN)20.9(COLUMN)297 Lily Ponds(COLUMN)33,132(COLUMN)23.4(COLUMN)328 Marshall Heights(COLUMN)28,379(COLUMN)15.7(COLUMN)264 Mass. Ave. Heights(COLUMN)210,925(COLUMN)21.9(COLUMN)2,746 Michigan Park(COLUMN)53,170(COLUMN)13.8(COLUMN)601 Mt. Pleasant(COLUMN)58,405(COLUMN)13.5(COLUMN)672 N. Cleveland Park(COLUMN)94,962(COLUMN)15.1(COLUMN)1,169 Observatory Circle(COLUMN)88,767(COLUMN)16.7(COLUMN)1,085 Old City #1 (Capitol East)(COLUMN)36,431(COLUMN)13.7(COLUMN)373 Old City #2 (Shaw-Dupont)(COLUMN)34,015(COLUMN)18.4(COLUMN)340 Palisades(COLUMN)86,307(COLUMN)27.2(COLUMN)1,051 Petworth(COLUMN)39,412(COLUMN)15.7(COLUMN)414 Randle Heights(COLUMN)32,936(COLUMN)14.7(COLUMN)326 R.L.A.(N.E.)(COLUMN)34,480(COLUMN)19.3(COLUMN)347 R.L.A. (S.W.)(COLUMN)60,215(COLUMN)6.3(COLUMN)697 Riggs Park(COLUMN)45,331(COLUMN)12.1(COLUMN)494 Shepherd Park(COLUMN)79,841(COLUMN)13.3(COLUMN)963 16th Street Heights(COLUMN)48,920(COLUMN)7.2(COLUMN)543 Spring Valley(COLUMN)167,935(COLUMN)15.2(COLUMN)2,162 Takoma Park,D.C.(COLUMN)41,799(COLUMN)8.4(COLUMN)446 Trinidad(COLUMN)30,178(COLUMN)18.1(COLUMN)288 Wakefield(COLUMN)72,995(COLUMN)34.2(COLUMN)870 Wesley Heights(COLUMN)131,403(COLUMN)28.6(COLUMN)1,665 Woodley(COLUMN)159,476(COLUMN)18.2(COLUMN)2.046 Woodridge(COLUMN)34,956(COLUMN)13.5(COLUMN)353 CITY AVERAGES(COLUMN)$ 56,959(COLUMN)18.6%(COLUMN)$ 652(END TABLE)