Mayor Marion Barry, who throughout his campaign exphasized property tax relief for city homeowners squeezed by rising assessments, formalluy proposed yesterday the first commercial property tax rate reduction in the District since 1975.

Barry asked the City Council to lower from $1.83 to $1.72 per $100 of assessed value the rate the city uses in computing taxes for the owners of $5.8 billion in commercial property. The 11-cent reduction would affect about half the $11.8 billion in taxable land in the District.

At the same time, Barry propesed a 10-cent reduction -- from $1.54 to $1.44 the rate for owner-occupied homes. He also proposed a $1.48 rate for a new class of properties -- those residental buildings of five units or less that are not owner-occupied.

"While the District government is under no obligation to reduce real property tax rates, I have repeatedly expressed my commitment to restricting unreasonable growth in real property tax revenues," Barry said in a letter tutlining the proposals.

"Enactment of my recommended tax rates will allow us to return in excess of $1.6 million to District residents and businesses."

Barry was careful not to call the proposals tax cuts, preferring instead to refer to them as measures to reduce "the impact of inflation in housing costs."

Adoption of the rates proposed by Barry would not prevent most homeowners from paying more property taxes in the tax year that began July 1 than were paid in the previous year.

For example, the owner of a house assessed for tax purposes at $50,00 last year paid about $631 in property taxes. Homes in the city have increased about 18 percent in assessed value since then, making the home now worth $59,000. Even with the rate reduction, the 1980 taxes would be $720 or $89 taxes would be taxes on that same house would be $770 -- or $139 more than in the previous year.

The owner of a house assessed at $70,000 last year would have paid about $939. This year, that homeowner would pay $1,059 or $120 more. If the rate were not reduced, taxes would be $194 more than the previous year. The new assessment would be about $82,600.

Earlier, city revenue officials projected that taxes could be lowered to $1.37 for owner-occupied homes, $1.43 for those not occupied by their owners and $1.78 for commercial properties.

However, the city law enacted last yr that establishes three classifications of tax rates prohibits a difference of more than 20 percent between the various rates. The $1.37 and $1.43 rates are between 25 and 30 percent lower than the $1.78 rate, Barry said.

The $1.44 tax rate proposed by Harry would be moderate when compared to others in the area. Arlington has a rate of $1.29, while the rate in Fairfax County is $1.54. The Alexandria tax rate is $1.44, the same proposed by Barry.

In suburban Maryland, where houses are taxed at only 45 percent of the assessed value, the tax rate is $3.04 in Prince George's County and $3.22 in Montgomery County.

In recent years, fair market values have generally run considerably below those of the assessed values used by tax agencies in most jurisdictions.