While the property tax remains the single most important local source of revenue for most Washington area jurisdictions, it is decreasing in importance as other money sources are found, a new study reports.

The study by the Metropolitan Washington Council of Government (COG), shows that 11 of 15 local governments surveyed relied less on the property tax in 1975 than in 1970, although in most cases the property tax still accounted for more than half of locally generated revenues.

Based on its study, COG concluded. "Local governments in the Washington area had begun to implement the principles behind Proposition 13 long before California voters approved the controversial amendment." The decline in the importance of property taxes reflects a national trend, the report added.

The COG survey found that while reliance on property taxes has been declining in most area governments, other local sources of money have been increasing in importance. It did not appear that any one single category "is taking up the slack," the COG report said.

For example, sales taxes were found to be an important source of revenue in the District and some Virginia suburbs, and income tax collections were found to be of increasing importance to the District and Montgomery and Prince George's counties. Falls Church relied heavily on fees collected for water sewer services.

The COG study was conducted by surveying the amount of locally generated revenues for each jurisdiction and determining the proportion of those revenues that came from property taxes. COG found that the property tax proportion of only four local governments in 1975 was the same as or more than it had been in 1970. Gaithersburg's proportion stayed nearly the same, Rockville's increased by about 2 percentage points, and Alexandria's increased by slightly more than 1 percentage point. Takoma Park showed an increase of almost 8 percent.

Jurisdictions surveyed in which property taxes accounted for more than half of locally generated revenues in 1975 were Prince George's County (53 percent), Gaithersburg (73 percent), Rockville (51 percent), Takoma Park (85 percent), College Park (57 percent), Loudoun County (71 percent) and Prince William County (61 percent).

In Montgomery County, 44 percent of local revenues came from property taxes. In the District, the figure was 23.5 percent; in Falls Church, 35 percent, and in Greenbelt, 49 percent.

The survey found that the property tax is the single most important local source of revenue in all jurisdictions except the District and Falls Church, but also that other taxes were becoming increasingly important. Sales taxes in the District, for example, accounted for almost 19 percent of local revenues, up more than 2 percent over the 1970 figure. Income taxes represented 28.4 percent of local revenues for D.C., the report said, 24.5 percent in Montgomery County, and 21.6 percent in Prince George's County in 1975.

COG grouped revenues from such sources as water, sewer, and refuse fees under the category "revenue from government enterprises," and found that they were important to some jurisdictions and not used in others.