The D.C. City Council gave preliminary approval yesterday to a property tax relief package that includes an automatic tax credit for $109 for most of the District's 100,000 homeowners.

The legislation does not guarantee, however, that homeowners will pay less taxes this year than last year. This is because residential property tax assessments in many city neighborhoods have soared, requiring homeowners to pay more in taxes than the $100 credit they will receive.

If the legislation voted on yesterday is enacted, it will work this way: the first $8,000 of any home's assessed value will be exempt from taxation. At the city's current tax rate of $1.83 per $100 of assessed value, the "credit" will be worth $109.80 to owners of single-family homes.

If a homeowner's new assessment is more than $6,000 above his old assessment, however, his total tax bill will still be greater this year than last.

Additional tax savings for elderly, blind and disabled persons earning $20,000 a year or less are also included in the legislation. An expanded "circuit breaker" tax relief plan in the tax package provides reductions of from 62 per cent to 93 per cent for elderly, blind and disabled homeowners.

Still further tax relief could come as the result of amendments anticipated when the bill comes up for final reading in two weeks. At that time, some Council members indicated yesterday, provisions may be added setting a ceiling on the percentage by which assessed home values (for tax purposes) can rise from year to year.

The tax relief plan would become effective immediately upon final passage, thereby reducing 1977 tax bills, which are payable in September, 1977, and March, 1978.

Enactment of the plan would mean that the city will get an estimated $13 million to $14 million less each year in residential property tax revenues. Most of that loss could be absorbed. Council tax relief supporters contend, because soaring assessments are bringing in a nearly equal amount of previously unanticipated revenues.

Approval of the tax relief plan yesterday capped several months of maneuvering over what appears to be emerging as one of the hottiest political issues in the city.

The measure passed unanimously by the Council was a compromise between a plan proposed by the Council's finance and revenue committee, chaired by Marion Barry (D-at large), and one put forth by Mayor Walter E. Washington.

Barry's proposal contained the $6,000 assessment exemption while the mayor's plan provided for a "circuit breaker" for all elderly homeowners, regardless of income. The compromise legislation approved yesterday included Barry's proposal as well as the circuit breaker, although a $20,000 yearly income limit was imposed.

The Council also added blind and disabled homeowners to those eligible for circuit breaker tax relief.

The assessment tax credit would apply only to residences in the city occupied by single families, leaving about 5,000 duplexes not covered, according to Council staff members' estimates.

Last year, the owner of a $40,000 home paid $732 in property taxes. This year, the owner of a home with an identical value would have a base tax of $622 - $110 less.

If that person additionally made less than $10,000 he would qualify for the regular "circuit breaker" tax relief that limits property tax payments according to income.

The owner of a $40,000 home who had an income of $10,000, for example would receive an additional tax credit of $177, thus paying only $445 in property taxes.

For blind, disabled or elderly persons - those 62 or older - the circuit breaker ceiling is $20,000 in annual income. The owner of a $40,000 home who fits into one of those categories, and, for instance, made $15,000 per year, would pay no more than $375 in property taxes.

The tax relief plan was one of two financial measures given preliminary approval by the Council yesterday. Both have far-reaching implications.

Legislation was also approved establishing a system by which the city will decide which local financial institutions will become depositories for an estimated $1.5 billion annually in city funds.

The city has traditionally kept its money in the U.S. Treasury. However, the 1974 home rule legislation allows the city to establish a system to transfer that money to local banks, savings and loans and other financial institutions.

The measure approved yesterday stipulates that as much as one-third of the city's funds should be set aside for deposit in financial institutions on the basis of their lending and hiring practices in the city.

The remaining money would be given to other institutions based on competitive bidding, with priority going to those that offer the city the best financial returns on its investments.

The set-aside provision virtually guarantees that the four minority-owned banks and savings and loans in the city will get the maximum allowable deposits from the city - amounts up to one-fourth of their current total deposits.

The four minority-owned institutions are: Industrial Bank of Washington, United National Bank, Independence Federal Savings and Loan and Community Federal Savings and Loan.

Those four institutions have total assets of about $100 million and thus would probably get no more than $33 million of the city's money. However, framers of the legislation think that would be of considerable help to these institutions, which have traditionally made more loans and mortgages in the District of Columbia and to low and moderate income persons, and also have better employment practices affecting minorities.

Yesterday's City Council session lasted almost four hours, and at one point was disrupted for nearly half an hour by a group of more than 40 protesters, most of whom represented the City Wide Housing Coalition.

The group tried in vain to get the Council to discuss a proposed revision of the city's rent control law that would permit some landlords to increase rent next year as much as 15 per cent.

The rent control bill was approved by the Council's housing committee last week but has not been scheduled for a floor debate. It was not on the agenda for yesterday's meeting. But a housing coalition spokesperson, saying that if the Council "cared about rent control," it should discuss the bill anyway.

Chanting "Stop the war on the poor, tenants can't afford no more" and waving self-styled "Wanted" posters for some Council members who support the rent control bill, the demonstrators shouted down Council Chairman Sterling Tucker for about 10 minutes. They left the Council chambers only after Tucker warned that they would be arrested if the demonstration continued.

The group then went out into the hallway and, stamping their feet and clapping their hands, continued for another 20 minutes, before leaving with assurances that "We'll be back."