The Montgomery County Council yesterday lopped a penny from the countywide residential property tax rate, but because of continued increases in property values, residents still will pay an average of 8.5 percent more in taxes when the bills go out in July.

The higher tax collection figure, set to fund the county's new $822.8 million budget passed by the council last month, was approved in a 5-to-1 vote with Council President David L. Scull dissenting. Council member William E. Hanna Jr. was absent.

Scull reiterated a position he took early in the budget sessions that the property tax increase would not be necessary were it not for the spiraling cost of employe pay packages that he maintains have outpaced inflation.

"Taxes are going up at more than double the rate of inflation," Scull said. "We are at that point because of the inevitable forward motion of the employe pay increases."

In its action yesterday, the council not only decreased the property tax rate by a cent, from $2.27 per $100 of assessed value to $2.26, but reduced the extra mass transit tax rate for Metro by a penny, from 19 cents to 18 cents per $100 of assessed value.

Taxes for recreation, garbage collection, the park and planning commission and downcounty fire districts all either stayed the same or were decreased slightly.

Nevertheless, most homeowner bills will increase anywhere from 5.5 to 11.5 percent because of increased property values and the county's complex system of triennial assessments.

For the 70,000 homeowners who received assessment notices last December, property assessments increased an average of 33 percent in Montgomery County--nearly the highest in the state--despite a widespread perception among homeowners that home prices have actually been holding steady, if not decreasing, over the past year. That feeling has been bolstered by the fact that assessments in all the neighboring jurisdictions either held steady or decreased for the first time in many years.

But unlike many other states, Maryland assesses one-third of its property each three years. In other words, the assessments received in December 1982, for example, covered a three-year period over which time housing prices jumped significantly. If housing prices did decrease in 1982, that decrease would have been offset by increases during the two previous years.

The triennial assessment plan was enacted by the state General Assembly in 1979 to cushion property owners against wild year-to-year jumps in housing values, and also to head off the kind of taxpayer revolt that swept California in the late 1970s and began popping up in Maryland counties.

With the new tax rate set yesterday, the owner of an average Montgomery home with a market value of $100,000 in fiscal year 1981 will find his property tax bill increased by either $90, $125, or $160, depending on the year in which the home was last assessed. Homeowners with the most recent assessments will get the greatest tax bill increases. Persons who were last reassessed two years ago will receive the smallest increases.