Real estate taxes due in September will drop for most of the 100,000 owners of single-family homes in Washington, but will rise slightly for others as a result of tax measures enacted last week by the D.C. City Council. The reduction from the 1977 tax bill will average $22 for each home.

The lower bills will result from new tax reform legislation and tax rates recommended by Mayor Walter E. Washington and Marion Barry (D-At Large), chairman of the council finance and revenue committee, who are rival mayora1 candidates.

The average city taxpayers occupies a home that increased from a 1977 value of $37,488 to a 1978 value of $44,837. That resident's tax bill this year will decline to $554 from last year's $576.

If the council had not passed the reform measure, the same taxpayer would have owed the city $599, an increase of $23 over 1977.

This year, taxpayers will get bills based on a combination of higher assessed value, an increased homeowner exemption that partly offsets the higher value and a lower tax rate. Half the bill must be paid in September, the other half by next March.

Last year's tax rate was $1.83 for each $100 of assessed value. This year's residential rate will be $1.54.

For owner-occupied homes, the first $9,000 of assessed value will not be taxed, compared with $6,000 last year. This means each qualified taxpayer will save $138 on his bill this year as a result of the exemption, compared with $109 last year.

But the saving will go only to those taxpayers who mailed an affidavit of owner-occupancy last spring to the D.C. Department of Finance and Revenue. For anyone who failed to do so, department officials say, it is now too late.

Because there are so many variables, notably in assessments, the tax measures produced by the mayor and council will have sharply uneven results across the city.

As the accompanying chart reflects, taxes will rise slightly for some homeowners in a few neighborhoods (such as LeDroit Park and Petworth) where increased assessments far outstripped the citywide average of 19.7 percent. For most homeowners, taxes will go down. Taxes in some of the city's most affluent neighborhoods will go down the most.

For example, on a home in Georgetown the average tax cut will be $234 fromlast year's $1,789 bill. This cut is precisely the same dollar amount as the entire $234 tax bill that will be owed in Brentwood, a working-class neighborhood in Northeast. The average Brentwood taxpayer's bill will drop $40 from last year.

There are several ways of stating the savings from the new tax program.

Barry has used the figure $13.9 million. That represents the difference between the expected yield from the new, lower tax rate of $1.54 and what Washingtonians would have paid if the old $1.83 rate had been kept in effect and applied to the 19.7 percent increase in assessed value.

Barry's figure also includes increased income tax credits that will be granted to lower the moderate-income families under an expanded "circuit breaker" program.

As people earning up to $20,000 annually pay higher taxes (sometimes indirectly, through rents), the rising tax burden figuratively trips a circuit breaker, permitting them to recover part of those taxes by filling out Scheduled H on next year's D.C. income tax form. That, however, will not affect what is owed now in real estate taxes.

For homeowners, the direct benefits of the council-passed tax program in real estate taxes alone will total around $3 million, or about 2 percent of the $156 million in residential real estate tax collections.

In an era of fast-rising prices and property values - the violatile kind of situation that produced Proposition 13 in California - even holding the line on taxes is considered by city officials to be no small feat.

For Washington homeowners, the biggest source of distress has been [WORD ILLEGIBLE] increasing assessments, raising [WORD ILLEGIBLE] of fast-escalating taxes. Property is now assessed at 100 percent of market value.

In 1976, assessments incresed 32 percent from the previous year. In 1977, they rose 42 percent. This year's increase of 19.7 percent actually represented an overall slowing of the upward trend. But, as the chart shows, there was a wide variation among neighborhoods. Those with the largest increases had not been reassessed for two years.

In the aggregate, higher assessments do not automatically mean higher taxes. In fact, a little-understood law passed by Congress before home rule went into effect in 1975 requires that as assessments rise the tax rate should proportionately, unless the council votes otherwise.

This means that Mayor Washington was required by law to recommend the lower $1.54 rate on residential property that was accepted by the council. Because of the level of increased assessments, any higher rate would have amounted to a tax increase, requiring a separate vote by the council.

The council approved one significant change for future years. It amended the congressional law to permit the city to collect increased revenue from real estate taxes, tied to the Labor Department's consumer price index.For example, if the index goes up 7 percent, the tax collections can rise similarly.

The mayor also recommended that the old $1.83 rate be kept for commercial property, including apartment houses, an action vehemently opposed by the business community. This will bring in an estimated $11 million in new revenues from commercial property.

That additional revenue more than offsets the $3 million loss from lower residential taxation and, according to Barry, makes possible the expanded circuit breaker.

Benefits under the circuit breaker are reckoned under a complex formula that relates the level of real estate taxation to a family's earned income. For example, someone earning $12,000 whose family lives in a home valued at $42,000 would be eligible for a credit of $277.